Question

please show me the sum step by step

Answer 1

$\sqrt{20} = \sqrt{(5 \times 4)} = \sqrt{5} \times \sqrt{4} = 2 \sqrt{5} \\ \sqrt{40} = \sqrt{(10 \times 4)} = \sqrt{10} \times \sqrt{4} = 2 \sqrt{10} \\ \sqrt{80} = \sqrt{(16 \times 5)} = \sqrt{16} \times \sqrt{5} = 4 \sqrt{5} \\in \: denominator \: of \: que \\ \sqrt{10} + 2 \sqrt{10} = \sqrt{10} (1 + 2) = 3 \sqrt{10} \\ 2 \sqrt{5} - \sqrt{5} - 4 \sqrt{5} = \sqrt{5} (2 - 1 - 4) = - 3 \sqrt{5} \\ now \: in \: equation \: \\ 15 \div (3 \sqrt{10} - 3 \sqrt{5} ) = 5 \times 3 \div 3( \sqrt{10} - \sqrt{5} ) = 5 \div ( \sqrt{10} - \sqrt{5} )$