a+b=2(a+b)^2=a^2+b^2+2ab=4a^2+b^2=4-2ab=4-2*2=01/2a³b+a²b²+1/2ab³=1/2ab(a^2+b^2)+(ab)^2=(ab)^2=2^2=4
原式=(ab/2)(a²+2ab+b²)=(ab/2)(a+b)²=(2/2)×2²=4
