geometrical proof of (a-b)^3
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Answer:
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Step-by-step explanation:
This can also be written as:
= (a + b) (a + b) (a + b)
Now, multiply first two binomials as shown below:
= { a(a + b) + b(a + b) } (a + b)
= { a2 + ab + ab + b2 } (a + b)
On rearranging the terms in curly braces we get:
= { a2 + b2 + ab + ab } (a + b)
= { a2 + b2 + 2ab } (a + b)
Now, multiply trinomial with binomial as shown below:
= a2(a + b) + b2(a + b) + 2ab(a + b)
= a3 + a2b + ab2 + b3 + 2ab(a + b)
= a3 + b3 + a2b + ab2 + 2ab(a + b)
= a3 + b3 + a2b + ab2 + 2ab(a + b)
Take ab common from the above red highlighted terms and we get:
= a3 + b3 + ab(a + b) + 2ab(a + b)
On adding like terms and we get:
= a3 + b3 + 3ab(a + b)
On solving it further we get:
a3 + b3 + 3a2b + 3ab2
Hence, in this way we obtain the identity i.e. (a + b)3 = a3 + b3 + 3ab(a + b) = a3 + b3+ 3a2b + 3ab2