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Confused_111
Nov 17, 2007, 07:26 PM
Hey there could would you work out the value of c in this.
The line y=4x-1 is tangent to the curve with the equation y=x^4+c. Find the value of "c"?
Thanks

terryg752
Nov 18, 2007, 12:36 AM
At the tangent, dy/dx = gradient of the tangent

For y = x^4 +c, dy/dx = 4x^3

For y=4x-1 , gradient = 4 (dy/dx = 4)

4x^3 = 4, hence x = 1

y = 4x - 1 = 3

(1, 3) must lie on

y = x^4 + c

3 = 1 + c

c = 2