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Expansions (Including Substitution) — MATHEMATICS STD 9 — Question

ICSE BoardEnglish MediumSTD 9MATHEMATICSExpansions (Including Substitution)2 Marks
Question
Expand :$ (3x + 5y + 2z) (3x - 5y + 2z)$
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Answer

$(3x+5y+2z) (3x-5y+2z)$
$= {(3x+2z)+(5y)} {(3x+2z)-(5y)}$
$= (3x+2z)^2-(5y)^2$
${since(a+b) (a-b)=a^2-b^2}$
$= 9x^2+4z^2+2 \times 3x\times 2z -25y^2$
$= 9x^2+4z^2+12xz- 25y^2$
$= 9x^2+4z^2-25y^2+12xz$

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