4x^2 + 9xy − y^2 = 8implicit differentiation
4x^2 + 9xy - y^2 = 88x + 9xf'(x) + 9y - 2yf'(x) = 0f'(x) (2y - 9x) = 8x + 9yf'(x) = (8x + 9y)/(2y - 9x)
