If 3x-4y=5 and xy = 3 fund the value of 27x^3- 64y^3 ....... (Chapter : Identities )
Please answer fast ...☝☝
mowjoshu:
The answer is 665 in the book .... seems like no is getting that answer .... me nither ... please try figuring out how we will get that ans ...
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Answered by
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Hi friend
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Your answer
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Given that : -
(3x - 4y) = 5 and xy = 3
To find : - value of 27x³ - 64y³ = ?
Now,
----------
3x - 4y = 5
On squaring both sides, we have
(3x - 4y)² = (5)²
=> 9x² + 16y² - 24xy = 25
=> 9x² + 16y² = 25 + (24 × 3)
=> 9x² + 16y² = 25 + 72
=> 9x² + 16y² = 97
Then ,
27x³ - 64y³
= (3x)³ - (4y)³
= (3x - 4y)(9x² - 12xy + 16y²)
= 5 × {(9x² + 16y²) - (12 × 3)}
= 5 × (97 - 36)
= 5 × 61
= 305
HOPE IT HELPS
---------------
Your answer
------------------
Given that : -
(3x - 4y) = 5 and xy = 3
To find : - value of 27x³ - 64y³ = ?
Now,
----------
3x - 4y = 5
On squaring both sides, we have
(3x - 4y)² = (5)²
=> 9x² + 16y² - 24xy = 25
=> 9x² + 16y² = 25 + (24 × 3)
=> 9x² + 16y² = 25 + 72
=> 9x² + 16y² = 97
Then ,
27x³ - 64y³
= (3x)³ - (4y)³
= (3x - 4y)(9x² - 12xy + 16y²)
= 5 × {(9x² + 16y²) - (12 × 3)}
= 5 × (97 - 36)
= 5 × 61
= 305
HOPE IT HELPS
The answer is given 665 in the book ..
yes
it will be 665
he has just gone with the formula a little bit wrong
3x-4y=5,xy=3,find 27x³-64y³
(a-b)³=a³-b³-3ab(a-b)(formula) (3x-4y)³=5³ (3x)³-(4y)³-3(3x)(4y)(3x-4y)=125 27x³-64y³-36(xy)(3x-4y)=125 27x³-64y³-36(3)(5)=125
27x³-64y³=125+540 27x³-64y³=665
27x³-64y³=125+540 27x³-64y³=665
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