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

1 Answer
Don't Memorise
Jun 12, 2015

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

Explanation:

#(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#

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