如果x,y为实数,那么x²+y²+6x-8y+30的值总是
A 正数 B复数 C非负数 D非正数
人气:218 ℃ 时间:2020-05-10 14:23:55
解答
x²+y²+6x-8y+30
=x^2+6x+9+y^2-8y+16+5
=(x+3)^2+(y-4)^2+5
所以恒为正数,选择A
此类题目都是用配方法解答的
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