problem with limit & derivative

i have problems with limit and derivative

first problem :

Code:

`l i m Cos X - Cos(X+h)`

h-->0 ---------------------

h

second one

Code:

`find dy/dx :`

third one :

Code:

`find points on curve y=tan(x/2) , x belong to ]0,360[ and the tangent is perpendicular to straight line 3x=8-3y`

i got 4 solutions in this problem .... 2 of them i think refused

Re: problem with limit & derivative

Quote:

Originally Posted by

**mido22**

Use the sum and difference formula for cosine.

Alternatively, recognize that

Quote:

Originally Posted by

**mido22** find dy/dx :

Differentiate implicitly and then solve for If you're really stuck, show us what you've tried.

Quote:

Originally Posted by

**mido22** find points on curve y=tan(x/2) , x belong to ]0,360[ and the tangent is perpendicular to straight line 3x=8-3y

i got 4 solutions in this problem .... 2 of them i think refused

I'm not even sure what this is saying. Are you looking for points on whose tangent lines are perpendicular to the given line, or what?

Re: problem with limit & derivative

for the third problem ..yes i 'm looking for points on whose tangent perpen. to 3x=8-3y

here is my attempt for the 2nd one :

Re: problem with limit & derivative

Re: problem with limit & derivative

Quote:

Originally Posted by

**mido22** for the third problem ..yes i 'm looking for points on

whose tangent perpen. to 3x=8-3y

What do we know about the slopes of perpendicular lines?

Re: problem with limit & derivative

the perpen . line equation : 3x=8-3y so its slope is -1

so the slope of tangent is -1 / -1 = 1

then i get x/2 =90 or 315 or 135 or 450

then i cancelled the 2nd and fourth solutions becz x belong to ]0,360[

is this right?

Re: problem with limit & derivative

and i get the solution of the 2nd problem

Re: problem with limit & derivative