X x(1-x)dx 4 120( ) ( ) 1 3 3 0 1 3 0 1 3 0 1 1 1 1 2 3 1 (1 ) 6 1 1 1 1 1 (1 ) . 6 6 4 5 120 x x x x dx x x dx x x dx ⎛ ⎞ = − ⎜ ⎟ − − ⎝ ⎠ = − ⎛ ⎞ = − = ⎜ ⎟ − = ⎝ ⎠ ∫ ∫ ∫