[tex]\sqrt h\cdot\sqrt{h^3}=\\
h^{\frac{1}{2}}\cdot \left(h^3\right)^{\frac{1}{2}}=\\
h^{\frac{1}{2}}\cdot h^{\frac{3}{2}}=\\
h^{\frac{1}{2}+\frac{3}{2}}=\\
h^{\frac{4}{2}}=\\
h^2[/tex]
or other way
[tex]\sqrt h\cdot\sqrt{h^3}=\\ \sqrt{h^4}=\\ \sqrt{(h^2)^2}=\\ |h^2|=\\ h^2 [/tex]
