Question

Упростите выражение (5 +√ 7) (√28 - 2)

Answer 1

$(5 + \sqrt{7} )( \sqrt{28} - 2) =\left(5+\sqrt{7}\right)\left(2\sqrt{7}-2\right) =10\sqrt{7}-10+2\left(\sqrt{7}\right)^{2}-2\sqrt{7} =10\sqrt{7}-10+2\times 7-2\sqrt{7} =10\sqrt{7}-10+14-2\sqrt{7} =10\sqrt{7}+4-2\sqrt{7} =8\sqrt{7}+4$

Answer 2

$(5+\sqrt7)(\sqrt{28}-2)=5\sqrt{28}-10+\sqrt{7\cdot28}-2\sqrt7=$

$=5\sqrt{7\cdot4}-10+\sqrt{196}-2\sqrt7=10\sqrt7-2\sqrt7-10+14=8\sqrt7+4$