Q50 / 90 · JEE Main 2023 (08 Apr Shift 2) · Mathematics

If domain of the function loge6x2+5x+12x-1+cos-12x2-3x+43x-5 is α,β∪γ,δ, then 18α2+β2+γ2+δ2 is equal to

Correct answer: 20

Solution

We need to find the domain of the function loge6x2+5x+12x-1+cos-12x2-3x+43x-5.

⇒6x2+5x+12x-1>0 .....(1) and

⇒ -1≤2x2-3x+43x-5≤1......(2)
Now From 1,
⇒6x2+5x+12x-1>0

⇒(3x+1)(2x+1)(2x-1)>0

Now we get the common region here as
⇒x∈-12,-13∪12,∞.......(a)

From 2 we get that
⇒-1≤2x2-3x+43x-5≤1

⇒2x2-3x+43x-5≥-1......3

and 2x2-3x+43x-5≤1.....4

From 3 we get
⇒2x2-3x+43x-5+1≥0

⇒x∈-12,12∪53,∞.....b

From 4 we get
⇒2x2-3x+43x-5-1≤0

⇒2x2-6x+93x-5≤0

As D=-62-429<0 and 2>0, we observe that 2x2-6x+9>0 ∀x∈ℝ
⇒13x-5≤0  ∵2x2-6x+9>0∀x∈R

⇒  x∈-∞,53   ......c

⇒ Intersection of (a), (b) and (c) gives us
x∈-12,-13∪12,12.

On comparing this with α,β∪γ,δ,
⇒α2+β2+γ2+δ2=109
⇒18α2+β2+γ2+δ2=20.

Hence this is the required answer.

Hence, the correct answer is 20.

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