Question
Evaluate: $(a + 5)(3a - 2)(5a + 1)$
✓
Answer
$(a + 5)(3a - 2)(5a + 1)$
$= {a (3a - 2) + 5(3a - 2)} (5a + 1)$
$= (3a^2 - 2a + 15a - 10)(5a + 1)$
$= (3a^2 + 13a - 10)(5a + 1)$
$= 5a (3a^2 + 13a - 10) + 1 (3a^2 + 13a - 10)$
$= 15a^3 + 65a^2 - 50a + 3a^2 + 13a - 10$
$= 15a^3 + 68a^2 - 37a - 10$
$= {a (3a - 2) + 5(3a - 2)} (5a + 1)$
$= (3a^2 - 2a + 15a - 10)(5a + 1)$
$= (3a^2 + 13a - 10)(5a + 1)$
$= 5a (3a^2 + 13a - 10) + 1 (3a^2 + 13a - 10)$
$= 15a^3 + 65a^2 - 50a + 3a^2 + 13a - 10$
$= 15a^3 + 68a^2 - 37a - 10$
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