1.0·49（x＋y）²
=49(x＋y)²／100
= 【 7／10(x＋y)】²
2.1／36（m－n）²
=[1／6(m－n)]²
3 .x²－y²＋10y
=(x＋y)(x－y)＋10y
将x+y=5代入上式有
(x＋y)(x－y)＋10y
=5（x－y）＋10y
=5x－5y＋10y
=5(x＋y)
=5×5
=25