=16-8+2x-8+2x-1/2x²=1/2x²+4x
16-1/2乘(4-x)乘4-1/2(4-x)乘4-1/2x^2=16-8+2x-8+2x-1/2x²=1/2x²+4x
16-1/2*(4-x)*4-1/2(4-x)*4-1/2x^2=16-8+2x-8+2x-1/2x²=1/2x²+4xjingrui
