tentukan hasil perkalian akar akar berikut! a. (3 √7 + 9) (3 √7 - 9)

[tex]$\begin{align} (3 \sqrt{7} + 9)(3 \sqrt{7} - 9) &= (3 \sqrt{7} )^2 - 9^2\\&= 3(7) - 81 \\&= -60 \end{align}[/tex]