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66

Given $x>0$, the value of $f(x)=-3 \cos \sqrt{3+x+x^2}$ lie in the interval .......... .

Explanation

Given function, $f(x)=-3 \cos \sqrt{3+x+x^2}$

We know that,

$$\begin{aligned} -1 \leq \cos x \leq 1 \\ \Rightarrow \quad -3 \leq 3 \cos x \leq 3 \\ \Rightarrow \quad 3 \geq-3 \cos x \geq-3 \\ \Rightarrow \quad -3 \leq-3 \cos x \leq 3 \end{aligned}$$

So, the value of $f(x)$ lies in $[-3,3]$.

67

The maximum distance of a point on the graph of the function $y=\sqrt{3} \sin x+\cos x$ from $X$-axis is ......... .

Explanation

Given that, $y=\sqrt{3} \sin x+\cos x$

$$\begin{aligned} y & =2\left[\frac{\sqrt{3}}{2} \sin x+\frac{1}{2} \cos x\right] \\ & =2\left[\sin x \cdot \cos \frac{\pi}{6}+\cos x \sin \frac{\pi}{6}\right] \\ & =2 \sin (x+\pi / 6) \end{aligned}$$

Graph of $y=2\sin x$

Hence, the maximum distance is 2 units.

68

In each of the questions 68 to 75 , state whether the statements is True or False? Also, give justification.

A
TRUE
B
FALSE
69

The equality $\sin A+\sin 2 A+\sin 3 A=3$ holds for some real value of $A$.

A
TRUE
B
FALSE
70

$\sin10\Upsilon$ is greater than $\cos10\Upsilon$.

A
TRUE
B
FALSE