## amonoconnor one year ago I'm stuck on this one... I just don't see how to manipulate or substitute to evaluate it without getting 0. Find the Limit of: *mathematical expression in first comment" Thank you! Any and all help is greatly appreciated!

1. amonoconnor

$\lim_{x \rightarrow \pi/4}\frac{ 1- \tan x }{\sin x - \cos x}$

2. amonoconnor

Sorry about the goofy fraction there, I retyped it twice, and the error didn't go away.

3. zepdrix

$\large\rm \frac{1-\color{orangered}{\tan x}}{\sin x-\cos x}=\frac{1-\color{orangered}{\frac{\sin x}{\cos x}}}{\sin x-\cos x}$Let's multiply top and bottom by cos(x) to get rid of that fraction up there.

4. zepdrix

$\large\rm =\frac{\cos x-\cos x\frac{\sin x}{\cos x}}{(\sin x-\cos x)\cos x}$

5. zepdrix

$\large\rm =\frac{\cos x-\sin x}{(\sin x-\cos x)\cos x}$Can you see where this is heading? :)

6. anonymous

I dont, Jesus. But good luck!!! <3 xD

7. amonoconnor

I understand everything up to here, but.. uhh, where do I go now? :/

8. zepdrix

Hmmm, let's factor a -1 out of each term in the numerator. It might click in your brain when we do :)

9. zepdrix

$\large\rm =\frac{-(\sin x-\cos x)}{(\sin x-\cos x)\cos x}$

10. zepdrix

Any ideas? Hmmmmm...

11. amonoconnor

.... and the -1 just goes in front of the "lim" part?

12. zepdrix

Ya, it can go where ever you want it to go :)

13. amonoconnor

Why don't we switch the signs in the denominator as well?

14. zepdrix

You mean when we factored out the -1? Or you're suggesting we should follow that up with another factoring of -1 in the bottom? I'm just a lil confused by the question >.<

15. amonoconnor

Yes, like, when you said we factor a -1 out of the top... why aren't we just taking it out of the whole fraction/problem, switching signs in the bottom to make it cosx(cosx - sinx)? Is it because -1 is technically = -1/+1?

16. zepdrix

Yes, good observation. If we did it to the whole thing, it would be more like -1/-1 being taken out, which is really no change at all.

17. zepdrix

I'm gonna color something and hopefully it jumps out at you as to why we took a -1 out of the numerator,$\large\rm =\frac{-(\color{orangered}{\sin x-\cos x})}{(\color{orangered}{\sin x-\cos x})\cos x}$

18. amonoconnor

I follow now.. I think I get it. So, now that I have this ... (hold on)

19. amonoconnor

$-1*\lim_{x \rightarrow \pi/4}\frac{1}{\cos(x)}$

20. amonoconnor

now that I have this, I just plug in pi/4?

21. zepdrix

So you were able to divide out "the problem piece", nice!

22. amonoconnor

= $(\sqrt{2})/2$

23. zepdrix

Hmm close. We're getting sqrt(2)/2, but that's in the denominator. And also, don't forget about your negative outside of the limit.

24. amonoconnor

right, so the "final answer" is...

25. amonoconnor

$-\frac{2}{\sqrt{2}}$

26. amonoconnor

?

27. zepdrix

Good, rationalize or simplify though

28. amonoconnor

Ahhh... touche. I was wondering how my book had just negative sqrt.2... Got it, multiply top and bottom by sqrt.2, cancel out the 2's , and we get -sqrt.2!! :D

29. zepdrix

wooo, nice job broski!

30. amonoconnor

Thanks again zepdrix! It's been a while, but your help is as helpful as ever!!

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