关与乘法公式设a<b<0,a平方+b平方=4ab,求
设a
a平方+b平方=4ab, ==> a^2-2ab+b^2=2ab (a-b)^2=2ab a^2+2ab+b^2=6ab (a+b)^2=6ab (a+b)^2/(a-b)^2=6ab/2ab=3 (a+b)/(a-b)=√3