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← JEE Main 2022 · 24 Jun · Shift 1
MathematicsSingle correct+4 / -1Question 6 of 90

JEE Main 2022 · 24 Jun · Shift 1, Mathematics question 6

The number of values of α\alpha for which the system of equations :
x+y+z=αx+y+z=\alpha
αx+2αy+3z=−1\alpha x+2\alpha y+3z=-1
x+3αy+5z=4x+3\alpha y+5z=4
is inconsistent, is

Choose one option
Answer and worked solution

Official answer: B

Determinant.
∣111α2α313α5∣=(10α−9α)−(5α−3)+(3α2−2α)=3(α−1)2.\begin{vmatrix}1&1&1\\\alpha&2\alpha&3\\1&3\alpha&5\end{vmatrix}=(10\alpha-9\alpha)-(5\alpha-3)+(3\alpha^2-2\alpha)=3(\alpha-1)^2.
Only α=1\alpha=1 can make the system inconsistent.

Check α=1\alpha=1. The equations are x+y+z=1x+y+z=1, x+2y+3z=−1x+2y+3z=-1, x+3y+5z=4x+3y+5z=4. Subtracting in pairs gives y+2z=−2y+2z=-2 and y+2z=5y+2z=5, a contradiction.

So exactly one value.

(B)