Uncertainty in Algebraic Substitution: Is X=0?

[Misr]

Homework Statement

[PLAIN]http://img137.imageshack.us/img137/4242/probhr.jpg


Well ,my problem is why after substitution for the first time the result os uncertainity (0/0)

Is X=0?

and I don't understand the step no 2

 

[vela]

What you've written doesn't make sense.

 

[Misr]

so...?

 

[Dick]

so...?

I think they mean the symbol you are writing as 'A' to be the symbol for pi.

 

[vela]

Go back and check that you accurately copied the original problem and the solution. It's pointless to try explain something that is wrong to begin with.

 

[Misr]

I think they mean the symbol you are writing as 'A' to be the symbol for pi.

awww you are right.The problem was written in another language so I translated it in a wrong way...I'll try to solve it again

Thanks for all of you

 

[Misr]

Ok..I'm back
so I know that sin(180-x)=sin(pi-x)

but x= pi right?
so sin(pi-x) = sin (x-pi) ?
why did we use sin(pi-x) instead ?
hope u could understand me
thanks

 

[Dick]

x doesn't equal pi. But for any x, sin(x)=sin(pi-x)=(-sin(x-pi)). Look at graph of the sin function or use a sin addition formula to prove that. They are using those identities to prove the limit.

 

[Misr]

x doesn't equal pi.

so why not?
isn't x-pi=0 as mentioned in the problem ?

 

[Dick]

so why not?
isn't x-pi=0 as mentioned in the problem ?

x-pi->0. That means x approaches pi (gets closer and closer to pi). It's not equal to pi. If x=pi then you have a zero in the denominator and the ratio is undefined.

 

[Misr]

oh ok thanks very much