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glewz

Posts: 781
Joined: Tue Jun 08, 2010 4:32 pm

stratocophic wrote:Not sure, but I think you can use DiffEQ to solve for the second solution, because the quadratic formula's obviously not going to work

You can't use differential equations - if you simplify first, you'd just get 2x - 2 = 0. Differentiate and you'd get 2 = 0. This answer is not significant either way (doesn't tell us whether we have a solution or not)

Take this problem/example:
x - 4 = 0
If you differentiate, you get 1 = 0. But we know that there's a solution (x = 4).

@ ptblazer NP. I was gonna write out the multiple ways to solve the above, but I thought it'd just be too much to read.

stratocophic

Posts: 2204
Joined: Tue Dec 22, 2009 6:24 pm

glewz wrote:
stratocophic wrote:Not sure, but I think you can use DiffEQ to solve for the second solution, because the quadratic formula's obviously not going to work

You can't use differential equations - if you simplify first, you'd just get 2x - 2 = 0. Differentiate and you'd get 2 = 0. This answer is not significant either way (doesn't tell us whether we have a solution or not)

Take this problem/example:
x - 4 = 0
If you differentiate, you get 1 = 0. But we know that there's a solution (x = 4).

@ ptblazer NP. I was gonna write out the multiple ways to solve the above, but I thought it'd just be too much to read.
lol this is why i'm in lawl school

ptblazer

Posts: 376
Joined: Sun Oct 31, 2010 11:27 pm

glewz wrote:You can't use differential equations - if you simplify first, you'd just get 2x - 2 = 0. Differentiate and you'd get 2 = 0. This answer is not significant either way (doesn't tell us whether we have a solution or not)

Take this problem/example:
x - 4 = 0
If you differentiate, you get 1 = 0. But we know that there's a solution (x = 4).

Haha, I'm enjoying how this thread has evolved. Taking the derivative and differential equations are two differen't things (although derivatives play an crucial role in differential equations), but point remains the same, neither can help you solve for x. Taking the derivative, which you've done in your example tells us the slope or in this case lack of slope. x-4=0 (x=4) is a straight vertical line, so the slope is undefined, which your answer of 1 = 0 shows us. Also any problem with only an x in it is going to give you an undefined answer (? = different ?) when you takes its derivative, because a derivative is taken with respect to something, generally Y in single varible calc. y = x + 4 for example, dx/dy = 1. This says the slope of that line is 1.
Again, I'm only responding because I like math and haven't been around it for a while, its not to be an ass.

glewz

Posts: 781
Joined: Tue Jun 08, 2010 4:32 pm

ptblazer wrote:
glewz wrote:You can't use differential equations - if you simplify first, you'd just get 2x - 2 = 0. Differentiate and you'd get 2 = 0. This answer is not significant either way (doesn't tell us whether we have a solution or not)

Take this problem/example:
x - 4 = 0
If you differentiate, you get 1 = 0. But we know that there's a solution (x = 4).

Haha, I'm enjoying how this thread has evolved. Taking the derivative and differential equations are two differen't things (although derivatives play an crucial role in differential equations), but point remains the same, neither can help you solve for x. Taking the derivative, which you've done in your example tells us the slope or in this case lack of slope. x-4=0 (x=4) is a straight vertical line, so the slope is undefined, which your answer of 1 = 0 shows us. Also any problem with only an x in it is going to give you an undefined answer (? = different ?) when you takes its derivative, because a derivative is taken with respect to something, generally Y in single varible calc. y = x + 4 for example, dx/dy = 1. This says the slope of that line is 1.
Again, I'm only responding because I like math and haven't been around it for a while, its not to be an ass.

I agree with these comments - I was trying to show that Diff equations can't be used in this case, and yes, you wouldn't derive with respect to x in my example. I was confused at how a poster was suggesting that Diff EQs would be used to solve this.

ptblazer

Posts: 376
Joined: Sun Oct 31, 2010 11:27 pm

betasteve wrote:Lololol. This was a comical thread. Only a law student could turn the OPs problem into something that would involve (and butcher) calculus.

haha. I was thinking the same thing, but I don't believe I butchered the calculus. I mean I better not have, considering how many times I've had to use it... but it's been a few years.

@glewz, yeah I was trying to support your statement, but I guess it got washed away by the wave of useless explanation.

glewz

Posts: 781
Joined: Tue Jun 08, 2010 4:32 pm

betasteve wrote:Lololol. This was a comical thread.

@ptblazer essential information - the legacy we give to future TLSers.

stratocophic

Posts: 2204
Joined: Tue Dec 22, 2009 6:24 pm

glewz wrote:
ptblazer wrote:
glewz wrote:You can't use differential equations - if you simplify first, you'd just get 2x - 2 = 0. Differentiate and you'd get 2 = 0. This answer is not significant either way (doesn't tell us whether we have a solution or not)

Take this problem/example:
x - 4 = 0
If you differentiate, you get 1 = 0. But we know that there's a solution (x = 4).

Haha, I'm enjoying how this thread has evolved. Taking the derivative and differential equations are two differen't things (although derivatives play an crucial role in differential equations), but point remains the same, neither can help you solve for x. Taking the derivative, which you've done in your example tells us the slope or in this case lack of slope. x-4=0 (x=4) is a straight vertical line, so the slope is undefined, which your answer of 1 = 0 shows us. Also any problem with only an x in it is going to give you an undefined answer (? = different ?) when you takes its derivative, because a derivative is taken with respect to something, generally Y in single varible calc. y = x + 4 for example, dx/dy = 1. This says the slope of that line is 1.
Again, I'm only responding because I like math and haven't been around it for a while, its not to be an ass.

I agree with these comments - I was trying to show that Diff equations can't be used in this case, and yes, you wouldn't derive with respect to x in my example. I was confused at how a poster was suggesting that Diff EQs would be used to solve this.
TBF I thought it was in the form where you had to use LaPlace transforms to solve it b/c you couldn't get all of the variables on one side, but I'm pretty sure you need two variables for that. Like I said, this is why I went to lawl school instead of chasing a Master's in engineering

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