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Find : "A"^3-1/"A"^3, If "A" -1/"A"=4. - Mathematics

Sum

Find : `"a"^3-1/"a"^3`, if `"a" -1/"a"=4`.

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Solution

`"a"  -1/"a"=4`

`⇒("a"-1/"a")^3=(4)^3`

`⇒"a"^3-1/"a"^3-3"a"xx1/"a"("a"-1/"a")=64`

`⇒"a"^3-1/"a"^3+3(4)=64` ........`[∵"a"-1/"a"=4]`

`⇒"a"^3-1/"a"^3-12=64`

`⇒"a"^3-1/"a"^3=64+12`

`⇒"a"^3-1/"a"^3=76`

Concept: Application of Formulae
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APPEARS IN

Selina Concise Mathematics Class 8 ICSE
Chapter 12 Identities
Exercise 12 (C) | Q 15 | Page 155
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