Find all points on the graph of y=1/4x^4+2/3x^3-5/2x^2+6x+7 where the slop of the tangent lins is 12.
dy/dx = x^3 +2x^2 -5x +6 = 12
x^3 + 2 x^2 - 5x -6 = 0
x = -3 , -1 , +2
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