Question
Use the direct method to evaluate : $(4+5x) (4−5x)$
✓
Answer
Note : $(a+b) (a−b)$
$= a^2 − b^2(4+5x) (4−5x)$
$= (4)^2 − (5x)^2$
$= 16 − 25x^2$
$= a^2 − b^2(4+5x) (4−5x)$
$= (4)^2 − (5x)^2$
$= 16 − 25x^2$
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