

InterviewSolution
Saved Bookmarks
1. |
The number of distinct real roots of `|(sinx, cosx, cosx),(cos x,sin x,cos x),(cos x,cos x,sin x)|=0` in the interval `-(pi)/4 le x le t (pi)/4` is |
Answer» Correct Answer - C We have, `|(sin x,cos x,cos x),(cos x,sin x,cos x),(cos x,cos x,sin x)| = 0` `rArr |(sin x + 2 cos x,sin x + 2 cos x,sin x + 2 cos x),(cos x,sin x,cos x),(cos x,cos x,sin x)| =0 " " ["Applying " R_(1) rarr R_(1) + R_(2) + R_(3)]` `rArr (sinx + 2 cos x) |(1,1,1),(cos x,sin x,cos x),(cos x,cos x,sin x)| = 0` `rArr (sinx + 2 cos x) |(1,0,0),(cos x,sin x - cos x,0),(cos x,0,sin x - cos x)| = 0 " " ["Applying " C_(3) rarr C_(3) - C_(1)"," C_(2) rarr C_(2) - C_(1)]` `rArr (sin x + 2 cos x) (sin x - cos x)^(2) = 0` `rArr tan x = -2 or, tan x = 1` `rArr x = (pi)/(4) " " [ :. x in [pi//4, pi//4] rArr -1 le tan x le 1]` |
|