Answer:
(x - 7)(x + 3)
Explanation:
[tex]\rightarrow \sf x^2 - 4x - 21[/tex]
breakdown
[tex]\rightarrow \sf x^2 - 7x +3x- 21[/tex]
factor out common terms
[tex]\rightarrow \sf x(x - 7) +3(x- 7)[/tex]
collect into groups
[tex]\rightarrow \sf (x+3)(x- 7)[/tex]
