(x^n)' = n*x^(n-1)
(с)' = 0
y = x⁷ + 1/6x⁶ - 20
y' = (x⁷ + 1/6x⁶ - 20)' = 7x⁶ + 6*1/6*x⁵ - 0 = 7x⁶ + x⁵
