Answer:
x = - 10 , x = 3
Explanation:
x² + 7x - 21 = 9 ( subtract 9 from both sides )
x² + 7x - 30 = 0 ← in standard form
consider the factors of the constant term (- 30) which sum to give the coefficient of the x- term (+ 7)
the factors are + 10 and - 3 , since
+ 10 × - 3 = - 30 and = 10 - 3 = + 7 , then
x² + 7x - 30 = 0
(x + 10)(x - 3) = 0 ← in factored form
equate each factor to zero and solve for x
x + 10 = 0 ( subtract 10 from both sides )
x = - 10
x - 3 = 0 ( add 3 to both sides )
x = 3
solutions are x = - 10 , x = 3