已知x+y=5,xy=3.求：①x²+y²；②（x-y）²
人气：489 ℃ 时间：2019-09-17 06:29:13
解答
x^2+y^2=(x+y)^2-2xy=5^2-2*3=25-6=19 (x-y)^2=(x+y)^2-4xy=5^2-3*4=25-12=13
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