Question

已知A分之1加B分之1等于A+B分之7,求A分之B加B分之A的值

Answer 1

1/a +1/b=7/(a+b) (a+b)/ab=7/(a+b) (a+b)^2=7ab a^2+b^2=5ab

b/a+a/b=(a^2+b^2)/ab=5