ACT Preparation / Unit 8 ACT 0705 short lesson, about 20 seconds
Sum Times Difference
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The idea
A sum times the difference of the same two terms gives the difference of their squares: (a + b)(a − b) = a² − b². The middle terms cancel.
In practice
(x + 7)(x − 7) = x² − 49; (3y + 2)(3y − 2) = 9y² − 4.
Where people slip
The two terms must match exactly; (x + 7)(x − 6) does not qualify.
Your place on the trail
Every lesson rests on earlier ones and opens later ones. Tap any to jump.
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