Ta có:
VT = 11 + 6√2
= 9 + 2.3.√2 + 2
= 3² + 2.3.√2 + (√2)²
= (3 + √2)²
= VP
Vậy 9 + 6√2 = (3 + √2)²
Ta có: \(VT=11+6\sqrt{2}\)
\(=9+6\sqrt{2}+2\)
\(=3^2+2\cdot3\cdot\sqrt{2}+\left(\sqrt{2}\right)^2\)
\(=\left(3+\sqrt{2}\right)^2=VP\left(đpcm\right)\)