# trig function differenciation

• Aug 5th 2012, 09:40 PM
arsenal12345
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 (Rofl)(Rofl)
• Aug 5th 2012, 10:27 PM
srirahulan
Re: trig function differenciation
What is y'',Can you explain?
• Aug 5th 2012, 10:35 PM
GJA
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).
• Aug 5th 2012, 10:50 PM
GJA
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!
• Aug 5th 2012, 11:10 PM
arsenal12345
Re: trig function differenciation
man i dont get it :( i am as lost as a nube can get
• Aug 5th 2012, 11:59 PM
richard1234
Re: trig function differenciation
What GJA is saying, find $y''$ given that $y = 3 \sin (2x + 3)$. Does $y'' + 4y$ always equal zero?
• Aug 6th 2012, 12:15 AM
arsenal12345
Re: trig function differenciation
no
• Aug 6th 2012, 12:53 AM
richard1234
Re: trig function differenciation
Are you sure?
• Aug 6th 2012, 01:04 AM
arsenal12345
Re: trig function differenciation
no not sure, can u please solve it and explain to me how u got ur answear ?
• Aug 6th 2012, 01:15 AM
jgv115
Re: trig function differenciation
Quote:

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 (Rofl)(Rofl)

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