S=x^2+(30-x)^2 咋算

问题描述:

S=x^2+(30-x)^2 咋算
S=x^2+(30-x)^2
咋算

S=x²+900-60x+x²
=2(x²-30x)+900
=2(x²-30x+225-225)+900
=2(x²-30x+225)-450+900
=2(x-15)²+450