Find a^3- b^3, if a-b=-7,ab=-10
Answers
Answer:
Solution:
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Given:
a - b = 10,
ab = 25,.
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To find:
The value of a³ - b³
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As, we know that,
(a - b)² = a² + 2ab + b²
=> a - b = 10,.
=> (a - b)² = (10)²
=> a² - 2ab + b² = 100
=> a² - 2(25) + b² = 100
=> a² - 50 + b² = 100
=> a² + b² = 100+50
=> a² + b² = 150,.....(ii),.
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We know that,
(a + b)² = a² + 2ab + b²
=> (a + b)²
=> a² + 2ab + b²
=> 150 + 2(25)
=> 150 + 50
=> 200
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=> (a + b)² = 200
=> a + b = 10√2 ...(iii)
Adding (i) & (ii), we get,
=> a + b + a - b = 10 + 10√2
=> 2a = 10 (√2 + 1)
=> a = 5(√2 + 1),...
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=> a + b = 10√2
=> 5√2 + 5 + b = 10√2
=> 5 + b = 10√2 - 5√2
=> 5 + b = 5√2
=> b = 5√2 - 5
=> b = 5(√2 - 1)
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We know that,
=> a³ - b³ = (a + b)(a² - ab + b²)
=> (5(√2+1) + 5(√2 -1))((5(√2 -1))² - 25 + (5(√2 - 1))²)
=> (5(√2 + 1 - √2 +1))(25(2 + 1 -2√2) - 25 + 25(2 +1 + 2√2))
=> 5 (2)( 25 ( 3 - 2√2) - 25 + 25 (3 - 2√2)
=> 5(2)( 25 (3 - 2√2 + 3 + 2√2 + 1)
=> 10(25(7))
=> 10 (175)
=> 1750,..
Step-by-step explanation:
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