Question

已知A-B=8,AB=12,(1)求A+B的值。(2)求A+B的值。大神们帮帮忙

Answer 1

（A-B)^2= A+B-2AB A+B=（A-B)^2+2AB=64+12*2=88 (A+B)^2=A+B+2AB=88+12*2=112 A+B=正负4根号7

Answer 2

A-B=8 AB=12 (A-B)=A-2AB+B=64， 所以A+B=64+2AB=64+2x12=88 (A+B)=A+2AB+B=88+2x12=112 A+B=√112=4√7