Subjective Type

Simplify : $$\sqrt {45} - 3\sqrt {20} + 4\sqrt {5}$$.

Solution

$$\sqrt {45}-3\sqrt {20}+4\sqrt {5}$$
$$=\sqrt {3\times 3\times 5}-3\sqrt {2\times 2\times 5}+4\sqrt {5}$$
$$=3\sqrt {5}--6\sqrt {5}+4\sqrt {5}$$
$$=7\sqrt {5}-6\sqrt {5}$$
$$=\sqrt {5}$$


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