Discussion
Factorise x² + x - 72
Answer: C
Find two numbers whose product is \( -72 \) and whose sum is \( +1 \).
\[ 9 \times (-8) = -72, \qquad 9 + (-8) = 1 \]
\[ x^{2} + x - 72 = (x - 8)(x + 9) \]
Checking: \( x^{2} + 9x - 8x - 72 = x^{2} + x - 72 \). Swapping the signs would give a middle term of \( -x \).
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