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Question
If a − b = 4 and ab = 21, find the value of a3 −b3
Solution
In the given problem, we have to find the value of `a^3 - b^3`
Given `a-b = -4,ab = 21`
We shall use the identity `(a-b)^3 = a^3- b^3 - 3ab(a-b)`
Here putting, a-b = - 4,ab = 21,
`(4)^3 = a^3 - b^3 - 3 (21) (4)`
`64 = a^3 - b^3 - 252`
`64 + 252 = a^3 -b^3`
`316 = a^3 - b^3`
Hence the value of `a^3 -b^3` is 316.
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