Let overrightarrow and overrightarrow d be vectors such that |overrightarrow +overrightarrow d|=√29 and overrightarrow ×(2 i+3 j+4 k)=(2 i+3 j+4 k) ×…
JEE Main 2026 — Mathematics Coordinate Geometry
2026mcqhard
Let c and d be vectors such that ∣c+d∣=29 and c×(2i^+3j^+4k^)=(2i^+3j^+4k^)×d. If λ1,λ2(λ1>λ2) are the possible values of (c+d)⋅(−7i^+2j^+3k^), then the equation K2x2+(K2−5K+λ1)xy+(3K+2λ2)y2−8x+12y+λ2=0 represents a circle, for K equal to :
Official previous-year question
Held on 21 Jan 2026 · Verified 6 Jul 2026.
Options
A
1
B
4
C
-1
D
2
Did you get this right?
Sign in to track your attempts and accuracy.
Solution
From c×a=a×d where a=2i^+3j^+4k^, we get (c+d)×a=0.
So c+d=ta. Given ∣c+d∣=29: ∣t∣⋅29=29, so t=±1.
(c+d)⋅(−7i^+2j^+3k^)=±(−14+6+12)=±4.
λ1=4, λ2=−4.
For circle: Coeff of x2 = Coeff of y2: K2=3K−2⇒K=1,2.
Coeff of xy=0: K2−5K+4=0⇒K=1,4.
Common value: K=1.
Your note
Sign in to keep a private note on this question. Nothing you write is ever public.