Statement-1: The system of linear equations … has a non-trivial solution for only one value of α lying in the interval (0, π 2 ). Statement-2: The…
JEE Main 2013 — Mathematics Algebra
2013mcqmedium
Statement-1: The system of linear equations x+(sinα)y+(cosα)z=0x+(cosα)y+(sinα)z=0x−(sinα)y−(cosα)z=0 has a non-trivial solution for only one value of α lying in the interval (0,2π). Statement-2: The equation in αcosαsinαcosαsinαcosα−sinαcosαsinα−cosα=0 has only one solution lying in the interval (0,2π)
Official previous-year question
Held on 23 Apr 2013 · Verified 6 Jul 2026.
Options
A
Statement-1 is true, Statement-2 is true, Statement-2 is not correct explantion for Statement-1.
B
Statement-1 is true, Statement-2 is true, Statement-2 is a correct explantion for Statement-1.
C
Statement-1 is true, Statement- 2 is false.
D
Statememt-1 is false, Statement-2 is true.
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Solution
⇒α=3×16x64x=34Δ1=111sinαcosα−sinαcosαsinαcosα=001sinα−cosαcosα+sinα−sinαcosα−sinαsinα−cosαcosα=(sinα−cosα)2−(cos2α−sin2α)=sin2α+cos2α−2sinα⋅cosα−cos2α=2sin2α−2sinα⋅cosα=2sin2α(sinα−cosα) Now, sinα−cosα=0 for only α∴Δ1=4π in (0,2π)=2(sinα)×0=0, since value of sinα is finite for α∈(0,2π) Hence non-trivivial solution for only one value of α in (0,2π)cosαsinαcosαsinαcosα−sinαcosαsinα−cosα=0⇒002cosαsinαcosα−sinαcosαsinα−cosα=0⇒2cosα(sin2α−cos2α)=0∴cosα=0 or sin2α−cos2α=0 But cosα=0 not possible for any value of α∈(0,2π)∴sin2α−cos2α=0⇒sinα=−cosα, which is also not possible for any value of α∈(0,2π) Hence, there is no solution.
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