Question

已知[m-n]的2次方=9,[m+n]的2次方=1,则m的2次方+n的2次方=??

Answer 1

m^2-2mn+n^2=9 m^2+2mn+n^2=1 两式相加得2(m^2+n^2)=10 m^2+n^2=5

Answer 2

(m-n)²=9
m²-2mn+n²=9 (1)
(m+n)²=1
m²+2mn+n²=1 (2)
(1）+（2）得：
2m²+2n²=9+1
m²+n²=5