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Question
Solve the following quadratic equation by factorisation method:
x2 + x – 20 = 0
Solution
x2 + x – 20 = 0
∴ x2 + 5x − 4x − 20 = 0
∴ x + 5x – 4x − 20 = 0
∴ x(x + 5) – 4(x + 5) = 0
∴ (x + 5)(x – 4) = 0
∴ (x + 5) = 0 or (x – 4) = 0
∴ x + 5 = 0 or x – 4 = 0
∴ x = – 5 or x = 4
∴ – 5 and 4 are roots of the given quadratic equation.
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