Find the first partial derivatives at a point

Question

f(x,y)= (x-4y)/(x+4y) at the point (x,y)=(3,4).

∂f/∂x(3,4)= ?

∂f/∂y(3,4)=?

Answer 1

∂f/∂x = [1(x + 4y) - 1(x - 4y)]/(x +, 4y)² = 8y/(x + 4y)², ∂f/∂x(3,4) = 8·4/(3 + 16)²/361 = 32/361

∂f/∂y = [-4(x + 4y) - 4(x - 4y)]/(x + 4y)² = - 8x/(x + 4y)²; ∂f/∂y(3, 4) = - 24/361