y = 4 x^2 -2 x
in general derivative of x^n = n x^(n-1) so
dy/dx = 4 * 2 x^1 - 2 x^0
8 x - 2
Now if you have not had that relation you have to do it from the definition
dy/dx = (y at x+h - y at x) /h as h-->0
y at x+h = 4 (x+h)^2 - 2 (x+h)
= 4 x^2 + 8 x h +4 h^2 - 2 x - 2 h
y at x = 4 x^2 - 2 x
difference over h = 8 x + 4 h - 2
as h-->0 that is
8 x - 2
as we already knew
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