Question

Factorise $9x^2-64$

• A. $(3x+8)(3x+8)$
• B. $(3x+8)(3x-8)$
• C. $(3x-8)(3x-8)$
• D. $(9x+4)(9x-4)$

Answer 1

The correct option is B

$(3x+8)(3x-8)$

Given $9x^2-64$

It can be written as

$(3x{)}^2-(8{)}^2$

Using difference of squares we have $a^2-b^2=(a+b)(a-b)$

Hence $a=3xandb=8$

$(3x{)}^2-(8{)}^2$ = $(3x+8)(3x-8)$