Quick Math Question

[isekii]

How do you solve

-.21 = log (0.2-x/x) ?

 

[royaldank]

As writen, x could be anything except 0 since x/x is 1.

 

[40Hands]

*shutters*

<----hates trig

 

[DingDingDao]

10^-.21 = (0.2-x)/x
.617 = (0.2-x)/x
.617x = 0.2-x
1.617x = 0.2
x = .124

 

[DingDingDao]

Originally posted by: BroeBo
*shutters*

<----hates trig

:laugh:
that's not trig...

 

[isekii]

Originally posted by: DingDingDao
10^-.21 = (0.2-x)/x
.617 = 0.2-x/x
.617x = 0.2-x
1.617x = 0.2
x = .124

Thank You!

 

[dullard]

Originally posted by: DingDingDao
10^-.21 = (0.2-x)/x
.617 = 0.2-x/x
.617x = 0.2-x
1.617x = 0.2
x = .124

Only 2 glaring math errors there. Good try though.

 

[TallBill]

Guh, you just reminded me that sooner or later I'll have to take trig for like the 4th time in my life.

 

[DingDingDao]

Originally posted by: dullard

Originally posted by: DingDingDao
10^-.21 = (0.2-x)/x
.617 = 0.2-x/x
.617x = 0.2-x
1.617x = 0.2
x = .124

Only 2 glaring math errors there. Good try though.

What two math errors?

 

[dullard]

Originally posted by: TallBill
Guh, you just reminded me that sooner or later I'll have to take trig for like the 4th time in my life.

Again, trig uses these: sine, cosine, and tangent. Or a slight variation of these. Log has nothing at all to do with trig.

Originally posted by: DingDingDao
What two math errors?

(1) Original post used (0.2 - x / x). You changed this to (0.2 - x) / x in your first line. However, in your second line you changed back to the correct answer. Together, I count this as one error.

(2) In your third line you multiplied by x. But (0.2 - x / x) *x = (0.2 * x - x). Somehow you came up with (0.2 - x) as the answer.

 

[DingDingDao]

Originally posted by: dullard

Originally posted by: TallBill
Guh, you just reminded me that sooner or later I'll have to take trig for like the 4th time in my life.

Again, trig uses these: sine, cosine, and tangent. Or a slight variation of these. Log has nothing at all to do with trig.

Originally posted by: DingDingDao
What two math errors?

(1) Original post used (0.2 - x / x). You changed this to (0.2 - x) / x in your first line. However, in your second line you changed back to the correct answer. Together, I count this as one error.

(2) In your third line you multiplied by x. But (0.2 - x / x) *x = (0.2 * x - x). Somehow you came up with (0.2 - x) as the answer.

1) I read his first post as a mistype. If you actually read it as 0.2-x/x, then the equation doesn't work at all, because the log of 0.2 (if x = 0) is -.70, and the log of -.8 (if x != 0) is invalid.

Also, I didn't change it back. I just removed the parenthesis after I removed the log, but the expression is the still the same. I'll correct it, but it doesn't change the math.

2) If the expression is (0.2-x)/x is multiplied by x, the resulting expression is 0.2-x.

3) Try my answer in his original equation. It works. If you try to solve it your way, you don't get the correct answer.

EDIT: I tried it your way (with 0.2x - x) and you get the equation 1.42x = 0, i.e. x=0. I already established that with x=0 the original equation fails.

This is a really simple algebraic equation. I don't understand why it seems to be so difficult for people to solve.

 

[dullard]

Originally posted by: DingDingDao
1) I read his first post as a mistype. If you actually read it as 0.2-x/x, then the equation doesn't work at all, because the log of 0.2 (if x = 0) is -.70, and the log of -.8 (if x != 0) is invalid.

Only the original poster can let us know if it is a mistype. In math you cannot just assume. Why not ask instead? As written, you are correct that there is no solution.

I just removed the parenthesis after I removed the log, but the expression is the still the same. I'll correct it, but it doesn't change the math.

(0.2 - x / x ) certainly is NOT the same as (0.2 - x) / x. That is a huge difference, the expression is not the same, and the math changes significantly.

2) If the expression is (0.2-x)/x is multiplied by x, the resulting expression is 0.2-x.

Correct, but you didn't have (0.2-x)/x in your second line.

 

[DingDingDao]

Originally posted by: dullard

Originally posted by: DingDingDao
1) I read his first post as a mistype. If you actually read it as 0.2-x/x, then the equation doesn't work at all, because the log of 0.2 (if x = 0) is -.70, and the log of -.8 (if x != 0) is invalid.

Only the original poster can let us know if it is a mistype. In math you cannot just assume. Why not ask instead? As written, you are correct that there is no solution.

I just removed the parenthesis after I removed the log, but the expression is the still the same. I'll correct it, but it doesn't change the math.

(0.2 - x / x ) certainly is NOT the same as 0.2 - x / x. That is a huge difference, the epxression is not the same, and the math changes significantly.

2) If the expression is (0.2-x)/x is multiplied by x, the resulting expression is 0.2-x.

Correct, but you didn't have (0.2-x)/x in your second line.

Thank you, Sgt. Math. I corrected the parenthesis error in the second line. Happy?
Regardless of the typing error, my answer is correct. If you can prove that I'm wrong, then show me.

 

[dullard]

Originally posted by: DingDingDao
Thank you, Sgt. Math. I corrected the parenthesis error in the second line. Happy?
Regardless of the typing error, my answer is correct. If you can prove that I'm wrong, then show me.

Ok now you are just down to one error: you solved a problem which isn't what the original poster asked. His has no answer, and yours does.

 

[b0mbrman]

Originally posted by: DingDingDao

Originally posted by: dullard

Originally posted by: DingDingDao
1) I read his first post as a mistype. If you actually read it as 0.2-x/x, then the equation doesn't work at all, because the log of 0.2 (if x = 0) is -.70, and the log of -.8 (if x != 0) is invalid.

Only the original poster can let us know if it is a mistype. In math you cannot just assume. Why not ask instead? As written, you are correct that there is no solution.

I just removed the parenthesis after I removed the log, but the expression is the still the same. I'll correct it, but it doesn't change the math.

(0.2 - x / x ) certainly is NOT the same as 0.2 - x / x. That is a huge difference, the epxression is not the same, and the math changes significantly.

2) If the expression is (0.2-x)/x is multiplied by x, the resulting expression is 0.2-x.

Correct, but you didn't have (0.2-x)/x in your second line.

Thank you, Sgt. Math. I corrected the parenthesis error in the second line. Happy?
Regardless of the typing error, my answer is correct. If you can prove that I'm wrong, then show me.

x/x = 1

Cheers :wine:

 

[ActuaryTm]

Originally posted by: dullard
(0.2 - x / x ) certainly is NOT the same as (0.2 - x) / x.

Indeed it is not.

However, 0.2 - x/x makes absolutely no sense given the equation criteria, as it would yield the log of a constant in an equation where the original poster was asked to solve for a variable.

Failure to look at the overall picture is a glaring error of the worst kind.

 

[Gibson486]

Originally posted by: ActuaryTm

Originally posted by: dullard
(0.2 - x / x ) certainly is NOT the same as (0.2 - x) / x.

Indeed it is not.

However, 0.2 - x/x makes absolutely no sense given the equation criteria, as it would yield the log of a constant in an equation where the original poster was asked to solve for a variable.

Failure to look at the overall picture is a glaring error of the worst kind.

i know.

Dullard, you are being teh high school math teacher from hell who nitpicks to make every student fail.

In the real world, you don't care what happens as long you your input gives you a desired output. Everything else in between are just the fillers. If you don't make assumptions, you will never finish the problem.

 

[DingDingDao]

Arrrrggghhhh. Paging Isekii....Isekii come in...can you please give everyone in the thread (including me) clarification on the original equation?

 

[dullard]

Originally posted by: Gibson486
Dullard, you are being teh high school math teacher from hell who nitpicks to make every student fail.

In the real world, you don't care what happens as long you your input gives you a desired output. Everything else in between are just the fillers.

In the real world, calculation mistakes lead to bridges collapsing, buildings falling, platforms giving way with 50 people on them, multimillion dollar space robots crashing, etc. Tons of money has been lost and people have been hurt or killed. All due to someone who didn't want to nitpick.

 

[vtqanh]

Originally posted by: DingDingDao
Arrrrggghhhh. Paging Isekii....Isekii come in...can you please give everyone in the thread (including me) clarification on the original equation?

he already submitted the solution, no more clarification needed:laugh:

 

[IAteYourMother]

Originally posted by: dullard

Originally posted by: TallBill
Guh, you just reminded me that sooner or later I'll have to take trig for like the 4th time in my life.

Again, trig uses these: sine, cosine, and tangent. Or a slight variation of these. Log has nothing at all to do with trig.

Originally posted by: DingDingDao
What two math errors?

(2) In your third line you multiplied by x. But (0.2 - x / x) *x = (0.2 * x - x). Somehow you came up with (0.2 - x) as the answer.

I'm absolutely sure that (.2-x/x) *x = (0.2-x)

 

[vtqanh]

Originally posted by: dullard

Originally posted by: Gibson486
Dullard, you are being teh high school math teacher from hell who nitpicks to make every student fail.

In the real world, you don't care what happens as long you your input gives you a desired output. Everything else in between are just the fillers.

In the real world, calculation mistakes lead to bridges collapsing, buildings falling, platforms giving way with 50 people on them, multimillion dollar space robots crashing, etc. Tons of money has been lost and people have been hurt or killed. All due to someone who didn't want to nitpick.

'kay

 

[DingDingDao]

Originally posted by: dullard

Originally posted by: Gibson486
Dullard, you are being teh high school math teacher from hell who nitpicks to make every student fail.

In the real world, you don't care what happens as long you your input gives you a desired output. Everything else in between are just the fillers.

In the real world, calculation mistakes lead to bridges collapsing, buildings falling, platforms giving way with 50 people on them, multimillion dollar space robots crashing, etc. In these cases tons of money has been lost and people have been hurt or killed. All due to someone who didn't want to nitpick.

Engineers have to make assumptions all the time. In virtually every engineering task, there are variables or factors that can't be directly measured. Models try to shed some light on what *might* be happening, but it can't directly account for sea-floor contouring during bridge building, or seismic activity below a building site. The last three houses my family lived in were new constructions, and I don't remember a single time a seismologist came to the lot to take seismic readings beneath the lot. They *assumed* the ground was stable.

 

[vtqanh]

Originally posted by: IAteYourMother

Originally posted by: dullard

Originally posted by: TallBill
Guh, you just reminded me that sooner or later I'll have to take trig for like the 4th time in my life.

Again, trig uses these: sine, cosine, and tangent. Or a slight variation of these. Log has nothing at all to do with trig.

Originally posted by: DingDingDao
What two math errors?

(2) In your third line you multiplied by x. But (0.2 - x / x) *x = (0.2 * x - x). Somehow you came up with (0.2 - x) as the answer.

I'm absolutely sure that (.2-x/x) *x = (0.2-x)

Did you fail algebra?

 

[dullard]

Originally posted by: IAteYourMother
I'm absolutely sure that (.2-x/x) *x = (0.2-x)

Quoted so it stays. Thanks for the laugh.