a^2+2*ab+b^2=15 (1)
a^2-2*ab+b^2=15 (2)
(1)+(2)=a^2+b^2=10(3)
(1)-(2)=ab=5
即a=5/b(4)代入（3）得
b=5时,a=-1
b=-5时,a=1
已知（a+b)²=15,（a-b)²=5,求a²+b²的值.
a^2+2*ab+b^2=15 (1)
a^2-2*ab+b^2=15 (2)
(1)+(2)=a^2+b^2=10(3)
(1)-(2)=ab=5
即a=5/b(4)代入（3）得
b=5时,a=-1
b=-5时,a=1