How do you multiply $(3sqrt2 - 9)(3sqrt2 +9)$ ?

Question

1316 views around the world

You can reuse this answer
Creative Commons License

Answer 1 · 2015-06-13T18:24:23

This is of the form $(a-b)(a+b) = a^2-b^2$ , so

$(3sqrt(2)-9)(3sqrt(2)+9) = (3sqrt(2))^2-9^2 = 18-81 = -63$

Standard difference of squares identity.

$(3sqrt(2)-9)(3sqrt(2)+9)$

$= (3sqrt(2))^2-9^2$

$= (3^2sqrt(2)^2)-9^2$

$=(9*2)-81 = 18-81 = -63$

How do you multiply (3sqrt2 - 9)(3sqrt2 +9)(3sqrt2 - 9)(3sqrt2 +9)?