Answer
$17\sqrt 2-15\sqrt 5$
Work Step by Step
$2\sqrt {50}-3\sqrt {125}+\sqrt {98}$
=$2\sqrt {2\times25}-3\sqrt {25\times5}+\sqrt {2\times49}$
=$2(\sqrt 2\times\sqrt {25})-3(\sqrt {25}\times\sqrt 5)+(\sqrt 2\times\sqrt {49})$
=$2(\sqrt 2\times5)-3(5\times\sqrt 5)+(\sqrt 2\times7)$
=$10\sqrt 2-15\sqrt 5+7\sqrt 2$
=$(10+7)\sqrt 2-15\sqrt 5$
=$17\sqrt 2-15\sqrt 5$
