Question

2√20-2√45+3√80
a)38√5
b)10√5
c)6√5
d)3√60

Answer 1

\[10\sqrt{5}\] ?

Answer 2

\[\sqrt{20}=\sqrt{4}\times \sqrt{5}=2 \sqrt{5}\]
\[\sqrt{45}=\sqrt{9}\times \sqrt{5}=3\sqrt{5}\]
\[\sqrt{80}=\sqrt{16}\sqrt{5}=4\sqrt{5}\]
so you have
\[2\times 2 \sqrt{5} - 2\times 3\sqrt{5}+3\times 4\sqrt{5}\]
\[=4\sqrt{5}-6\sqrt{5}+12\sqrt{5}\]
\[=10\sqrt{5}\]