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Expansions — MATHEMATICS STD 9 — Question

ICSE BoardEnglish MediumSTD 9MATHEMATICSExpansions3 Marks
Question
Find the cube of: $2a - 5b$
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Answer

Using $(a - b)^3$
$= a^3 - b^3 - 3ab (a - b)$
$(2a - 5b)$
$= (2a)^3- (5b)^3 - 3(2a) (5b) (2a - 5b)$
$= 8a^3 - 125b^3 - 30ab (2a - 5b)$
$= 8a^3- 125b^3 - 60a^2b + 150ab^2.$

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