Question

(x-9)(x+9) find the product

Answer 1

Method 1.

Use $(a-b)(a+b)=a^2-b^2$

$(x-9)(x+9)=x^2-9^2=x^2-81$

Method 2.

Use distributive property: (a + b)(c + d) = ac + ad + bc + bd

$(x-9)(x+9)=(x)(x)+(x)(9)+(-9)(x)+(-9)(9)=x^2+9x-9x-81=x^2-81$