1) f(x) = sinx + cosx , f'(x)= cosx - sinx , f'(0) = cos0 - sin0 = 1 - 0 = 1
2) y=1/4 * x⁴ - 2/3 * x³ + 1/2 * x² - x + 2
y' = x³ - 2x² + x - 1 , y'(-1)= -1 - 2 - 1 - 1 = -5
3) y=( x²+1 ) ( x³-1 ) ,
y' = 2x ( x³-1 ) + 3x² ( x²+1 ) = 2x⁴ - 2x + 3x⁴ + 3x² = 5x⁴ + 3x² - 2x
y'(1) = 5 + 3 - 2 = 6