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Expansions (Including Substitution) — MATHEMATICS STD 9 — Question

ICSE BoardEnglish MediumSTD 9MATHEMATICSExpansions (Including Substitution)2 Marks
Question
Find the cube of : $5a + 3b$
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Answer

$( a + b )^3 = a^3 + 3ab( a + b ) + b^3$
$( 5a + 3b)^3 = (5a)^3 + 3 \times 5a \times 3b( 5a + 3b) + (3b)^3$
$= 125a^3 + 45ab( 5a + 3b ) + 27b^3$
$= 125a^3 + 225a^2b + 135ab^2 + 27b^3$

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