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If a + b + c = 2s, then find the value of: (s – a)³ + (s – b)³ + 3(s – a)(s – b)(c)
Question

If a + b + c = 2s, then find the value of:
(s – a)³ + (s – b)³ + 3(s – a)(s – b)(c)

A.

2s

B.

ac

C.


D.


Correct option is D

Given:
a + b + c = 2s
Expression to simplify: (sa)3+(sb)3+3(sa)(sb)c(s - a)^3 + (s - b)^3 + 3(s - a)(s - b)c​​
Concept Used:
The given expression resembles the identity for the sum of cubes:
x3+y3+3xy(z)=(x+y)3x^3 + y^3 + 3xy(z) = (x + y)^3​​
where x = (s - a), y = (s - b), and z = c.
Solution:
Let x = s - a and y = s - b. The expression becomes:
(sa)3+(sb)3+3(sa)(sb)c=x3+y3+3xyc(s - a)^3 + (s - b)^3 + 3(s - a)(s - b)c = x^3 + y^3 + 3xyc​​
By the identity, this simplifies to:
(x+y)3=(sa+sb)3(x + y)^3 = (s - a + s - b)^3​​
Now,
x + y = (s - a) + (s - b) = 2s - (a + b)
Using a + b + c = 2s, we get:
a + b = 2s - c
So:
x + y = 2s - (2s - c) = c
So, (x+y)3=c3(x + y)^3 = c^3​​
Therefore, the value of the expression is c3.\bf c^3.​​

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