if a-b=4 and ab=21find a^3-b^3
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a-b = 4
ab = 21
a³-b³ = ?
=> (a-b)² = a²+b²-2ab
=> (4)² = a²+b²-2(21)
=> 16 = a²+b²-42
=> 16+42 = 58 => a²+b²
a³-b³ = (a-b)(a²+b²+ab)
=> a³-b³ = 4(58+21) => 4(79) => 316
hope this helps
ab = 21
a³-b³ = ?
=> (a-b)² = a²+b²-2ab
=> (4)² = a²+b²-2(21)
=> 16 = a²+b²-42
=> 16+42 = 58 => a²+b²
a³-b³ = (a-b)(a²+b²+ab)
=> a³-b³ = 4(58+21) => 4(79) => 316
hope this helps
Answered by
0
a-b=4
doing cube of both side ,we get
(a-b)^3=4^3
a^3-b^3-3ab (a-b)=64
a^3-b^3-3×21 (4)=64
a^3-b^3-252=64
a^3-b^3=64+252
a^3-b^3=316 ANSWER
doing cube of both side ,we get
(a-b)^3=4^3
a^3-b^3-3ab (a-b)=64
a^3-b^3-3×21 (4)=64
a^3-b^3-252=64
a^3-b^3=64+252
a^3-b^3=316 ANSWER
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