Question

select a suitable identity and find the following products
$(3t+9s)(3t-9s)$

Answer 1

$(3t+9s)(3t-9s)$

Using identity: $(a+b)(a-b)=a^2-b^2$

Therefore,

$(3t+9s)(3t-9s)$

$={\left(3t\right)}^2-{\left(9s\right)}^2$

$=9t^2-81s^2$