Math Help - differentiation and integration

1. differentiation and integration

I am reallly confused with this question, it seems so easy, but i still don't know what it is
the question is:

if dy/dx= cos3x and y=1 when x=0, find y when x=pi/4. I know the answer is supposed to be negative sqrt 0.5 but how to get there is whats confusing me.

2. Re: differentiation and integration

Originally Posted by supp
I am reallly confused with this question, it seems so easy, but i still don't know what it is
the question is:

if dy/dx= cos3x and y=1 when x=0, find y when x=pi/4. I know the answer is supposed to be negative sqrt 0.5 but how to get there is whats confusing me.

$y = \frac{\sin(3x)}{3} + C$
sub in the given values for x and y and solve for the constant of integration ... then evaluate the function at $x = \frac{\pi}{4}$