(7+3√5)(7-3√5)= ?

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Answer 1 · 2018-02-18T05:58:41

#4#

#(7+3 sqrt5)(7-3 sqrt5)#

#color(blue)((a+b)(a-b) = a^2 - b^2#

#(7+3 sqrt5)(7-3 sqrt5) = 7^2 - (3 sqrt5)^2#

#=49 - 3^2 sqrt5^2#

#=49 - 9 xx 5#

#=49 - 45#

#=4#

Answer 2 · 2018-02-18T05:59:00

The result is #4#.

#color(white)=(7+3sqrt5)(7-3sqrt5)#

#=7^2-7*3sqrt5+7*3sqrt5-(3sqrt5)^2#

#=49-21sqrt5+21sqrt5-3^2sqrt5^2#

#=49color(red)cancel(color(black)(-21sqrt5+21sqrt5))-9*5#

#=49-45#

#=4#