Question
Factorise: $a^2+6 a-91$
✓
Answer
$a^2+6 a-91$
$=a^2+13 a-7 a-91$
${-91 = 13 × (-7), 6 = 13 - 7}$
$= a(a + 13) - 7(a + 13)$
$ = (a + 13)(a - 7)$
$=a^2+13 a-7 a-91$
${-91 = 13 × (-7), 6 = 13 - 7}$
$= a(a + 13) - 7(a + 13)$
$ = (a + 13)(a - 7)$
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