Q.

If the domain of the function f(x)=cos-1(2x-511-3x)+sin-1(2x2-3x+1) is the interval [α,β] then α+2β is equal to:            [2026]

1 5  
2 2  
3 3  
4 1  

Ans.

(3)

f(x)=cos-1(2x-511-3x)+sin-1(2x2-3x+1)

-1≤2x-511-3x≤1

-1≤2x2-3x+1≤1

2x2-3x+2≥0,   2x2-3x≤0

x∈[0,32]    ..........(i)

2x-511-3x+1≥0     2x-511-3x-1≤0

2x-5+11-3x11-3x≥0    5x-1611-3x≤0

6-x11-3x≥0

x∈(-∞,165]∪(113,∞)

x∈(-∞,113)∪(6,∞)

Intersection:

x∈(-∞,165]∪[6,∞)    ....(ii)

Intersection of (i) & (ii) x∈[0,32]

α=0,  β=32  ⇒  α+2β=3