a) Ta có \(a\left(b+1\right)+b\left(a+1\right)=\left(a+1\right)\left(b+1\right)\Rightarrow2ab+a+b=a+b+ab+1\)
=> ab=1
b) Ta có \(2\left(a+1\right)\left(b+1\right)=\left(a+b\right)\left(a+b+2\right)\Leftrightarrow2ab+2a+2b+2=a^2+ab+2a+b^2+ab+2b\)
=> a^2+b^2=2
^_^
a(b+1) +b(a+1) = (a+1) (b+1) [2.(a+1)(a+b)] = (a+b)(a+b+2 )
=ab+a+ab+b =ab+a+b+1 =2a2+2ab+2a+2b = a2+ab+2a+ab+b2+2b
=ab = ab+a+b+1- ab -a-b =2a2 = a2+2ab+2a+b2+2b-2ab-2a-2b
=ab =1 =2a2 = a2+b2
Bấm đúng cho mình nha ! Hình như bạn chép sai đầu bài ở ý B :a2+b2=2a2 mà