y*cos(y)
Apply the product rule:
f(y)=yf{\left(y \right)} = yf(y)=y; to find ddyf(y)\frac{d}{d y} f{\left(y \right)}dydf(y):
Apply the power rule: yyy goes to 111
g(y)=cos(y)g{\left(y \right)} = \cos{\left(y \right)}g(y)=cos(y); to find ddyg(y)\frac{d}{d y} g{\left(y \right)}dydg(y):
The derivative of cosine is negative sine:
The result is: −ysin(y)+cos(y)- y \sin{\left(y \right)} + \cos{\left(y \right)}−ysin(y)+cos(y)
The answer is:
-y*sin(y) + cos(y)
-(2*sin(y) + y*cos(y))
-3*cos(y) + y*sin(y)