Answer:
(x - 7)(x + 3) = 0
Explanation:
To factorise the quadratic
Consider the factors of the constant term (- 21) which sum to give the coefficient of the x- term (- 4)
The factors are - 7 and + 3, since
- 7 × 3 = - 21 and - 7 + 3 = - 4, thus
(x - 7)(x + 3) = 0 ← in factored form