[tex]\displaystyle (2x+y)^2=(2x)^2+2 \cdot2x \cdot y+y^2=4x^2+4xy+y^2 \\ \\ \left(5x-y^2\right)^2=(5x)^2-2 \cdot 5x \cdot y^2+\left(y^2\right)^2=25x^2-10xy^2+y^4 \\ \\ \left( \sqrt{2a} +6 \right)^2=\left( \sqrt{2a} \right)^2+2 \cdot \sqrt{2a} \cdot 6+6^2=2a+12 \sqrt{2a} +36[/tex]
