Answer :
[tex](2a^2b)^2=2^2(a^2)^2b^2=4a^{2\cdot2}b^2=4a^4b^2\\\\Used:(x\cdot y)^n=x^n\cdot y^n\ and\ (x^n)^m=x^{n\cdot m}[/tex]
[tex]{ \left( 2{ a }^{ 2 }b \right) }^{ 2 }\\ \\ =\left( 2{ a }^{ 2 }b \right) \left( 2{ a }^{ 2 }b \right) \\ \\ =2\cdot 2\cdot { a }^{ 2 }\cdot { a }^{ 2 }\cdot b\cdot b\\ \\ =4{ a }^{ 4 }{ b }^{ 2 }[/tex]