Mathematics
Factorise the following:
y2 - 7y - 18
Factorisation
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Answer
To factorise y2 - 7y - 18, we want to find two real numbers whose sum is -7 and product is -18. By trial, we see that -9 + 2 = -7 and -9 × 2 = -18.
∴ y2 - 7y - 18 = y2 - 9y + 2y - 18
= y2 - 9y + 2y - 18
= y(y - 9) + 2(y - 9)
= (y - 9)(y + 2).
Hence, y2 - 7y - 18 = (y - 9)(y + 2).
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