(x+2y)二次方-10(x+2y)+25

(x+2y)²-10(x+2y)+25=(x+2y-5)²9（2x-y）²-6(2x-y)+1=(3(2x-y)-1)²=(6x-3y-1)²(x+a)²-6(x+a)(x-b)+9(x-b)²=(x+a-3x+3b)²=(a+3b-2x)²（p+q）²-2r(p+q)+r²=(p+q-r)²这些题目考的都是(a-b)²=a²-2ab+b²