Homework Help: math

Posted by David on Thursday, April 1, 2010 at 11:03pm.

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).

math - Reiny, Thursday, April 1, 2010 at 11:18pm
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
math - Hi, Tuesday, April 6, 2010 at 7:59pm
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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