Question

14．已知|x+2y+3|與（2x+y）²的值互為相反數(shù)，則x-y=3．

Answer 1

分析 根據(jù)非負(fù)數(shù)的性質(zhì)：幾個(gè)非負(fù)數(shù)的和等于0，則每個(gè)數(shù)等于0，即可列出關(guān)于x和y的方程，求得x和y的值，進(jìn)而求得代數(shù)式的值．

解答 解：根據(jù)題意得：$\left\{\begin{array}{l}{x+2y+3=0}\\{2x+y=0}\end{array}\right.$，
解得$\left\{\begin{array}{l}{x=1}\\{y=-2}\end{array}\right.$．
則原式=1+2=3．
故答案是3．

點(diǎn)評(píng) 本題考查了非負(fù)數(shù)的性質(zhì)：幾個(gè)非負(fù)數(shù)的和等于0，則每個(gè)數(shù)等于0，理解性質(zhì)是關(guān)鍵．