(7+3√5)(7-3√5)= ?

2 Answers
Feb 18, 2018

4

Explanation:

(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

Feb 18, 2018

The result is 4.

Explanation:

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