A graphing calculator is recommended. (a) If G(x) = 5x2 - x', find G'(a) and use it to find equations of the tangent lines to the curve y = 5x - x at the points (3, 18) and (4, 16). G'(a) = passing through (3, 18) y 1 ( x ) = passing through (4, 16) y, (x) =