f(x) = x² + 3x - 1
f '(x) = (x²)' + 3(x)' - 1' = 2x + 3
f(x) = x³(4 + 2x - x²) = 4x³ + 2x⁴ - x⁵
f '(x) = 4(x³)' + 2(x⁴)' - (x⁵)' = 12x² + 8x³ - 5x⁴
f(x) = x²(3x + x³) = 3x⁴ + x⁵
f '(x) = 3(x⁴)' + (x⁵)' = 12x³ + 5x⁴
f(x) = x² - 3x
f '(x) = (x²)' - 3(x)' = 2x - 3
f '(1/2) = 2 * 1/2 - 3 = - 2
f '(2) = 2 * 2 - 3 = 1
