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 - 2)(y + 9).
Hence, y2 + 7y - 18 = (y - 2)(y + 9).
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