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Consider f(x)=sin⁡(3x)+4,∀x∈Rf(x) = \sin(3x) + 4, \forall x \in \mathbb{R}. Then

(A) Maximum value of f(x)f(x) is 5

(B) Minimum value of f(x)f(x) is 3

(C) Maximum value of f(x)f(x) is attained at x=π6x = \frac{\pi}{6}

(D) Minimum value of f(x)f(x) is attained at x=0x = 0

Choose the correct answer from the options given below:

Solution

✅ Correct Option: 1

The function is f(x)=sin⁡(3x)+4f(x) = \sin(3x) + 4

The sine function satisfies −1≤sin⁡(3x)≤1-1 \leq \sin(3x) \leq 1 for all x∈Rx \in \mathbb{R}.

Adding 4 throughout:

−1+4≤sin⁡(3x)+4≤1+4-1 + 4 \leq \sin(3x) + 4 \leq 1 + 4

3≤f(x)≤53 \leq f(x) \leq 5

Therefore:

Maximum value of f(x)=5f(x) = 5 (when sin⁡(3x)=1\sin(3x) = 1)

Minimum value of f(x)=3f(x) = 3 (when sin⁡(3x)=−1\sin(3x) = -1)

Statement (A) is TRUE - Maximum value is 5

Statement (B) is TRUE - Minimum value is 3


For statement (C), the maximum occurs when sin⁡(3x)=1\sin(3x) = 1.

sin⁡(θ)=1\sin(\theta) = 1 when θ=π2\theta = \frac{\pi}{2}

3x=π23x = \frac{\pi}{2}

x=π6x = \frac{\pi}{6}

At x=π6x = \frac{\pi}{6}:

f(π6)=sin⁡(3×π6)+4f(\frac{\pi}{6}) = \sin(3 \times \frac{\pi}{6}) + 4

=sin⁡(π2)+4= \sin(\frac{\pi}{2}) + 4

=1+4= 1 + 4

=5= 5

Statement (C) is TRUE - Maximum is attained at x=π6x = \frac{\pi}{6}


For statement (D), at x=0x = 0:

f(0)=sin⁡(3×0)+4f(0) = \sin(3 \times 0) + 4

=sin⁡(0)+4= \sin(0) + 4

=0+4= 0 + 4

=4= 4

The minimum value is 3, not 4.

The minimum occurs when sin⁡(3x)=−1\sin(3x) = -1, which happens when 3x=3π23x = \frac{3\pi}{2}, giving x=π2x = \frac{\pi}{2}.

Statement (D) is FALSE - Minimum is not attained at x=0x = 0


Statements (A), (B), and (C) are correct.

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