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Functions question

2024 · 30 Jan · Shift 1 · Q48
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Functions question

2024 · 30 Jan · Shift 1 · Q48

JEE MainMathematicsFunctionsMCQ+4 / −1
If the domain of the function f(x)=cos⁡−1(2−∣x∣4)+{log⁡e(3−x)}−1f(x)=\cos ^{-1}\left(\frac{2-|x|}{4}\right)+\left\{\log _e(3-x)\right\}^{-1}f(x)=cos−1(42−∣x∣​)+{loge​(3−x)}−1 is [−α,β)−{γ}[-\alpha, \beta)-\{\gamma\}[−α,β)−{γ}, then α+β+γ\alpha+\beta+\gammaα+β+γ is equal to :
  1. A
    11
  2. B
    12
  3. C
    9
  4. D
    8
View written solutionFree

Correct answer: A

  1. We need the domain of f(x)=cos⁡−1(2−∣x∣4)+{ln⁡(3−x)}−1.f(x)=\cos^{-1}\left(\frac{2-|x|}{4}\right)+\left\{\ln(3-x)\right\}^{-1}.f(x)=cos−1(42−∣x∣​)+{ln(3−x)}−1.

So both parts must be defined.


  1. Domain from the inverse cosine term: cos⁡−1(u)\cos^{-1}(u)cos−1(u) is defined when −1≤u≤1.-1\le u\le 1.−1≤u≤1.

Here, u=2−∣x∣4.u=\frac{2-|x|}{4}.u=42−∣x∣​. So, −1≤2−∣x∣4≤1.-1\le \frac{2-|x|}{4}\le 1.−1≤42−∣x∣​≤1. Multiply throughout by 444: −4≤2−∣x∣≤4.-4\le 2-|x|\le 4.−4≤2−∣x∣≤4.

Now solve both sides:

  • From −4≤2−∣x∣,-4\le 2-|x|,−4≤2−∣x∣, we get −6≤−∣x∣  ⟹  ∣x∣≤6.-6\le -|x| \implies |x|\le 6.−6≤−∣x∣⟹∣x∣≤6.

  • From 2−∣x∣≤4,2-|x|\le 4,2−∣x∣≤4, we get −∣x∣≤2  ⟹  ∣x∣≥−2,-|x|\le 2 \implies |x|\ge -2,−∣x∣≤2⟹∣x∣≥−2, which is always true.

Hence the condition from the first term is ∣x∣≤6  ⟹  x∈[−6,6].|x|\le 6 \implies x\in[-6,6].∣x∣≤6⟹x∈[−6,6].


  1. Domain from the second term: {ln⁡(3−x)}−1=1ln⁡(3−x).\left\{\ln(3-x)\right\}^{-1}=\frac{1}{\ln(3-x)}.{ln(3−x)}−1=ln(3−x)1​.

For this to be defined:

  • logarithm must exist: 3−x>0  ⟹  x<3,3-x>0 \implies x<3,3−x>0⟹x<3,
  • denominator must be nonzero: ln⁡(3−x)≠0.\ln(3-x)\ne 0.ln(3−x)=0.

Now, ln⁡(3−x)=0  ⟹  3−x=1  ⟹  x=2.\ln(3-x)=0 \implies 3-x=1 \implies x=2.ln(3−x)=0⟹3−x=1⟹x=2. So we must exclude x=2x=2x=2.

Thus the condition from the second term is x<3,x≠2.x<3,\quad x\ne 2.x<3,x=2.


  1. Intersect both conditions:

From step 2: x∈[−6,6]x\in[-6,6]x∈[−6,6]

From step 3: x<3x<3x<3 and x≠2x\ne 2x=2

Therefore, Domain=[−6,3)−{2}.\text{Domain}=[-6,3)-\{2\}.Domain=[−6,3)−{2}.

Comparing with the given form [−α,β)−{γ},[-\alpha,\beta)-\{\gamma\},[−α,β)−{γ}, we get α=6,β=3,γ=2.\alpha=6,\quad \beta=3,\quad \gamma=2.α=6,β=3,γ=2.

Hence, α+β+γ=6+3+2=11.\alpha+\beta+\gamma=6+3+2=11.α+β+γ=6+3+2=11.


  1. Option check:
  • A: 111111 ✅
  • B: 121212
  • C: 999
  • D: 888

So the correct option is A.

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