How do you multiply $(3+sqrt7) (2-7sqrt7)$ ?

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Answer 1 · 2015-06-12T16:27:22

$=color(blue)( - 43 - 19sqrt7$

$(3+sqrt7) (2-7sqrt7)$

$= color(red)((3.2) - (3.7sqrt7)) + color(blue)((sqrt7 . 2) - sqrt(7).7sqrt7$
$= color(red)( 6 -21sqrt7) + color(blue)(2sqrt7 - 49$

Combining the like terms

$= color(red)(6-49) +color(blue)(2sqrt7 - 21sqrt7)$

$=color(blue)( - 43 - 19sqrt7$

How do you multiply (3+sqrt7) (2-7sqrt7)(3+sqrt7) (2-7sqrt7)?