Question
Use the direct method to evaluate : $(3x^2+5y^2) (3x^2−5y^2)$
✓
Answer
$(a+b) (a−b) $
$= a^2 − b^2(3x^2+5y^2) (3x^2−5y^2) $
$= (3x^2)^2 − (5y^2)^2$
$= 9x^4 − 25y^4$
$= a^2 − b^2(3x^2+5y^2) (3x^2−5y^2) $
$= (3x^2)^2 − (5y^2)^2$
$= 9x^4 − 25y^4$
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