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**Answer:**

1. x = -4 or x = 5

2. x = 3 or x = -7

**Step-by-step explanation:**

<u>1. x^2 - x - 20 = 0</u>

⇒ x^2 - x - 20 = 0

⇒ x^2 + 4x - 5x - 20 = 0

⇒ x (x + 4) - 5 (x + 4) = 0

⇒ (x + 4) (x - 5) = 0

⇒ (x + 4) = 0 or (x - 5) = 0

⇒ x = -4 or x = 5 ------> final solution

<u>2. x^2 + 4x - 21 =0</u>

⇒ x^2 + 4x - 21 = 0

⇒ x^2 - 3x + 7x - 21 = 0

⇒ x (x - 3) + 7 (x - 3) = 0

⇒ (x - 3) (x + 7) = 0

⇒ (x - 3) = 0 or (x + 7) = 0

⇒ x = 3 or x = -7 ------> final solution

**Answer:**

21.....i think!!!!

**Step-by-step explanation:**

hmmm lets see other answers

Vertex is –b/<span>2a, hope this helps:) just plug the numbers into that formula and BOOM</span>

**Answer:**

2

**Step-by-step explanation:**