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Question
Solve by completing the square:
x2 − x − 20 = 0
Sum
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Solution
Given:
x2 − x − 20 = 0
(−4) + (5) = 1
(−4) × (5) = −20
(x + 4) (x − 5) = x2 − x − 20
x2 + x − 20 = 0
Product = −20
Sum = +1
Numbers are +5 and –4
x2 + 5x − 4x − 20 = 0
⇒ (x + 5) (x − 4) = 0
x = −5 or x = 4
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