Answer
The first step $\sqrt{4\cdot 18}$ is wrong and the correct answer is $6 \sqrt{2}$
Work Step by Step
The given expression is
$=\sqrt{72}$
Factor as square terms.
$=\sqrt{4\cdot 9 \cdot 2}$
Use product property of square roots.
$=\sqrt{4}\cdot \sqrt{9} \cdot \sqrt{2}$
Use $4=2^2$ and $9=3^2$.
$=\sqrt{2^2}\cdot \sqrt{3^2} \cdot \sqrt{2}$
Simplify.
$=2\cdot 3 \cdot \sqrt{2}$
Multiply.
$=6 \sqrt{2}$
Hence, the first step $\sqrt{4\cdot 18}$ is wrong and the correct answer is $6 \sqrt{2}$
