Answer:
a = -6
b = 1
Step-by-step explanation:
The gradient of the tangent to the curve y = ax + bx^3, will be:
dy/dx = a + 3bx²
at (2, -4)
dy/dx = a+3b(2)²
dy/dx = a+12b
Since the gradient at the point is 6, then;
a+12b = 6 ....1
Substitute x = 2 and y = -4 into the original expression
-4 = 2a + 8b
a + 4b = -2 ...2
a+12b = 6 ....1
Subtract
4b - 12b = -2-6
-8b = -8
b = -8/-8
b = 1
Substitute b = 1 into equation 1
Recall from 1 that a+12b = 6
a+12(1) = 6
a = 6 - 12
a = -6
Hence a = -6, b = 1
