33091中３・平方根・計算問題・加法と減法1

$(1)$答$5\sqrt{5}$

$\begin{array}{rcl}2\sqrt{5}+3\sqrt{5}& =& (2+3)\times \sqrt{5}\\ & =& 5\sqrt{5}\end{array}$

$(2)$答$2\sqrt{7}$

$\begin{array}{rcl}3\sqrt{7}-\sqrt{7}& =& (3-1)\times \sqrt{7}\\ & =& 2\sqrt{7}\end{array}$

$(3)$答$0$

$\begin{array}{rcl}\sqrt{10}+\sqrt{10}-2\sqrt{10}& =& (1+1-2)\times \sqrt{10}\\ & =& 0\end{array}$

$(4)$答$-\sqrt{6}$

$\begin{array}{rcl}4\sqrt{6}-6\sqrt{6}+\sqrt{6}& =& (4-6+1)\times \sqrt{6}\\ & =& -\sqrt{6}\end{array}$

$(5)$答$13\sqrt{15}$

$\begin{array}{rcl}8\sqrt{15}-\sqrt{15}+6\sqrt{15}& =& (8-1+6)\times \sqrt{15}\\ & =& 13\sqrt{15}\end{array}$