Answer
$-40+10\sqrt {7a}-8\sqrt {2}+3\sqrt {14a}$
Work Step by Step
$\sqrt {14a}-(10+\sqrt {8})(4-\sqrt {7a})$
=$\sqrt {14a}-[10(4-\sqrt {7a})+\sqrt {8}(4-\sqrt {7a})]$
=$\sqrt {14a}-(40-10\sqrt {7a}+4\sqrt {8}-\sqrt {8\times7a})$
=$\sqrt {14a}-40+10\sqrt {7a}-4\sqrt {4\times2}+\sqrt {4\times2\times7a}$
=$\sqrt {14a}-40+10\sqrt {7a}-4(2)\sqrt {2}+2\sqrt {14a}$
=$-40+10\sqrt {7a}-8\sqrt {2}+2\sqrt {14a}+\sqrt {14a}$
=$-40+10\sqrt {7a}-8\sqrt {2}+3\sqrt {14a}$
