Consider the following two statements. Statement $\boldsymbol{p}$ : The value of $\sin 120^{\circ}$ can be…

Consider the following two statements. Statement $\boldsymbol{p}$ : The value of $\sin 120^{\circ}$ can be divided by taking $\theta=240^{\circ}$ in the equation $$ 2 \sin \frac{\theta}{2}=\sqrt{1+\sin \theta}-\sqrt{1-\sin \theta} . $$ Statement $\boldsymbol{q}$ : The angles $A, B, C$ and $D$ of any quadrilateral $A B C D$ satisfy the equation $$ \cos \left(\frac{1}{2}(A+C)\right)+\cos \left(\frac{1}{2}(B+D)\right)=0 $$ Then the truth values of $p$ and $q$ are respectively.
  1. $\mathrm{F}, \mathrm{T}$
  2. $\mathrm{T}, \mathrm{T}$
  3. F, F
  4. T, F

Solution

Statement $p$ : $ \sin 120^{\circ}=\cos 30^{\circ}=\frac{\sqrt{3}}{2} \Rightarrow 2 \sin 120^{\circ}=\sqrt{3} $ So, $\sqrt{1+\sin 240^{\circ}}-\sqrt{1-\sin 240^{\circ}}=$ $ \sqrt{\frac{1-\sqrt{3}}{2}}-\sqrt{\frac{1+\sqrt{3}}{2}} \neq \sqrt{3} $ Statement $\mathbf{q}$ : So, $A+B+C+D=2 \pi$ $ \begin{aligned} &\Rightarrow \frac{A+C}{2}+\frac{B+D}{2}=\pi \\ &\Rightarrow \cos \left(\frac{A+C}{2}\right)+\cos \left(\frac{B+D}{2}\right) \\ &=\cos \left(\frac{A+C}{2}\right)-\cos \left(\frac{A+C}{2}\right)=0 \end{aligned} $ Therefore, statement $p$ is false and statement $q$ is true

Asked in: JEE Main 2018 (15 Apr Shift 2 Online)

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