Question

Cho:   a+b=11, ab=30

Tính:    \(\left(a+b\right)^2;\left(a-b\right)^2;a^2+b^2\) 

Answer 1

+) \(\left(a+b\right)^2=11^2=121\)

+) Có: \(a+b=11\)

\(\Rightarrow\left(a+b\right)^2=121\)

\(\Rightarrow a^2+b^2+2ab=121\)

\(\Rightarrow a^2+b^2=121-2ab=121-2\cdot30=61\)

Nên: \(\left(a-b\right)^2=a^2+b^2-2ab=61-2\cdot30=1\)

+)\(a^2+b^2=61\) (làm phần b)

Answer 2

Ta có: \(\left(a+b\right)^2=\left(a+b\right)\left(a+b\right)=11.11=121\)