Q.
If a,b and c are non-zero real numbers and if the system of equations (a−1)x=y+z,(b−1)y=z+x and (c−1)z=x+y have a non-trivial solution, then 2a3+2b3+2c3 is equal to
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Answer: 1.5
Solution:
System of equations can be written as (a−1)x−y−z=0 x−(b−1)y+z=0 x+y−(c−1)z=0
Using Cramer's rule, for non-trivial solution Δ=0 ∣∣(a−1)11−1−(b−1)1−11−(c−1)∣∣=0 ⇒(a−1)[(b−1)(c−1)−1]−(−1)[−(c−1)−1]−1[1+b−1]=0 ⇒(a−1)[bc−b−c]−c−b=0 ⇒abc−ab−ac−bc+b+c−c−b=0 ⇒ab+bc+ca=abc⇒(a1+b1+c1)=1