Help me fast correct answer will get brainlest

a

Step-by-step explanation:

AB is just labeled as a, so it is already in terms

AB = a

Let me know if you don't know how or why..

D

Step-by-step explanation:

Given

a² - 36 = 5a ( subtract 5a from both sides )

a² - 5a - 36 = 0

Consider the factors of the constant term (- 36) which sum to give the coefficient of the a- term (- 5)

The factors are - 9 and + 4 , since

- 9 × + 4 = - 36 and - 9 + 4 = - 5 , then

(a - 9)(a + 4) = 0 ← in factored form

Equate each factor to zero and solve for a

a - 9 = 0 ⇒ a = 9

a + 4 = 0 ⇒ a = - 4

solution is { - 9, 4 } → D