math
posted by David .
4. For the curve with y = 2x3 + x  6, find:
(b.) the gradient at the point (1, 5)
(c.) the equation of the tangent line at the point (1, 5).

y = 2x^3 + x  6
dy/dx = 6x + 1
at (1,5), dy/dx = 6(1) + 1 = 7
so y = 7x + b
at (1,5)
5 = 7(1) + b
b = 12
equation of tangent is y = 7x  12 
y = 2x^3 + x  6
dy/dx = 6x + 1
at (1,5), dy/dx = 6(1) + 1 = 7
so y = 7x + b
at (1,5)
5 = 7(1) + b
b = 12
equation of tangent is y = 7x  12
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