If the domain of the function f(x)=cos−1(11−3x2x−5)+sin−1(2x2−3x+1) is the interval [α,β], then α+2β is equal to :
(A)1
(B)3✓ Correct
(C)5
(D)2
Answer: (B)
Solution
For sin−1(2x2−3x+1) the argument must lie in [−1,1]: the lower bound 2x2−3x+2≥0 holds for all x, while the upper bound 2x2−3x≤0 gives 0≤x≤23. On this interval 11−3x>0, and −1≤11−3x2x−5≤1 reduces to x≤516 and x≤6, both already satisfied. Hence the domain is [0,23], so α=0,β=23 and α+2β=3.
JEE Main · 2026 · 21 Jan 2026 · Shift 1 · Single correct option