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If x + 1/x= 7 then …

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If x + 1/x= 7 then find tge value of x³+ 1/x³

Posted by V Siva 5 years, 5 months ago

CBSE > Class 09 > Mathematics

2 answers

Sia ? 5 years, 5 months ago

It is given that ,
x + 1/x = 7
We know the algebraic identity,
a³ + b³ + 3ab ( a + b ) = ( a + b )³
or
a³ + b³ = ( a + b )³ - 3ab( a + b )
x³ + 1/x³ = (x + 1/x )³- 3 × x ×1/x(x + 1/x )
= ( x + 1/x )³ - 3( x + 1/x )
= 7³ - 3 × 7
= 7( 7² - 3 )
= 7 ( 49 - 3 )
= 7 × 46
= 322

1Thank You

V Siva 5 years, 5 months ago

The*

0Thank You

ANSWER

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CBSE > Class 09 > Mathematics