the tangent of the curve is determined by getting the first derivative of teh equation of the curve and substituting with the given data. in this case, the derivative of y=ax^3 is y' = 3a x^2. when x is equal to 5, y' = 3a (25) = 75 a
x=5; y = 125 a
y-y1 = m(x-x1)
y-125 a = 75 a (x-5)
y = 75 ax -500
-2x + y = b
-2(75/2) x + y = -500
a = 75/2
b = -500