The tricky part about the product rule is remembering to use it. f(x)*g(x) = f(x)g'(x) + f'(x)g(x)
k(x,y) = x^(2)sin(5x+4y)
k_x(x,y) = x^(2)*5*cos(5x+4y) + 2xsin(5x+4y)
= 5x^(2)cos(5x+4y) + 2xsin(5x+4y)
k_y(x,y) = x^(2)*4*cos(5x+4y) + x^(2)sin(5x+4y)
= 4x^(2)cos(5x+4y) + x^(2)sin(5x+4y)
g(x,y) = 3y^(2)e^(2x^(4))
g_x(x,y) = 3y^(2)*8x^(3)e^(2x^(4))
h(x,y) = xe^(5x^(2)+2y)
h_x(x,y) = x*10x(e^(5x^(2)+2y)) + e^(5x^(2)+2y)(1)
= 10x^(2)e^(5x^(2)+2y) + e^(5x^(2)+2y)