# Math Help - trig function differenciation

1. ## trig function differenciation

if y= 3sin(2x+3) show that y"+4y=0

and

if y= sinx + 2cosx show that y", + y""+y, +y =O

can some1 explain to me how to do these and solve them

k thnx

2. ## Re: trig function differenciation

What is y'',Can you explain?

3. ## Re: trig function differenciation

Hi, srirahulan. To answer your question, y'' is the second derivative of the function we are considering - in this case y=3sin(2x+3).

4. ## Re: trig function differenciation

Hi, arsenal12345. What we need to do is compute the second derivative y'' of y=3sin(2x+3) first. Then add 4y to what we get and see if it does equal zero. Does this answer your question? Good luck!

5. ## Re: trig function differenciation

man i dont get it i am as lost as a nube can get

6. ## Re: trig function differenciation

What GJA is saying, find $y''$ given that $y = 3 \sin (2x + 3)$. Does $y'' + 4y$ always equal zero?

no

8. ## Re: trig function differenciation

Are you sure?

9. ## Re: trig function differenciation

no not sure, can u please solve it and explain to me how u got ur answear ?

10. ## Re: trig function differenciation

Originally Posted by arsenal12345
if y= 3sin(2x+3) show that y"+4y=0

and

if y= sinx + 2cosx show that y", + y""+y, +y =O

can some1 explain to me how to do these and solve them

k thnx
For the first one:

$y'=6\cos(2x+3)$
$y'' = -12\sin(2x+3)$

Therefore... $LHS=y''+4y=-12\sin(2x+3)+4(3sin(2x+3))=0=RHS$

Do the same for the second one