Question : Two chords of lengths $a$ metre and $b$ metre subtend angles $60^{\circ}$ and $90^{\circ}$ at the centre of the circle, respectively. Which of the following is true?
Option 1: $b=\sqrt{2}a$
Option 2: $a=\sqrt{2}b$
Option 3: $a=2b$
Option 4: $b=2a$
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Correct Answer: $b=\sqrt{2}a$
Solution : The length of a chord in a circle, $=2×r×\sin \left(\frac{\theta}{2}\right)$ Where $r$ is the radius of the circle and $\theta$ is the angle subtended at the centre by the chord. Given that the lengths of the chords are $a$ and $b$ meters, they subtend angles of $60^{\circ}$ and $90^{\circ}$ at the centre of the circle respectively. $ \therefore a = 2 ×r ×\sin \left(\frac{60^{\circ}}{2}\right) = 2× r ×\sin30^{\circ}$...(i) $ \therefore b = 2×r× \sin \left(\frac{90^{\circ}}{2}\right)= 2×r× \sin45^{\circ}$...(ii) From equation (i) and (ii), $⇒\frac{a}{2 ×\sin30^{\circ}} = \frac{b}{2× \sin45^{\circ}}$ $⇒a = b \times \frac{\sin30^{\circ}}{\sin45^{\circ}}$ $⇒a=b×\frac{1}{\sqrt{2}}$ $⇒b=\sqrt{2}a$ Hence, the correct answer is $b=\sqrt{2}a$.
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Question : Two men standing on the same side of a pillar, 75 metres high, observe the angles of elevation of the top of the pillar to be $30^{\circ}$ and $60^{\circ}$, respectively. The distance between the two men is:
Option 1: $100\sqrt{3}$ m
Option 2: $100$ m
Option 3: $50\sqrt{3}$ m
Option 4: $25\sqrt{3}$ m
Question : Two chords $\mathrm{AB}$ and $\mathrm{CD}$ of a circle with centre $\mathrm{O}$, intersect each other at $\mathrm{P}$. If $\angle\mathrm{ AOD}=100^{\circ}$ and $\angle \mathrm{BOC}=70^{\circ}$, then the value of $\angle \mathrm{APC}$ is:
Option 1: $80^{\circ}$
Option 2: $75^{\circ}$
Option 3: $85^{\circ}$
Option 4: $95^{\circ}$
Question : In a circle of radius 3 cm, two chords of length 2 cm and 3 cm lie on the same side of a diameter. What is the perpendicular distance between the two chords?
Option 1: $\frac{4 \sqrt{3}-3 \sqrt{2}}{2}$ cm
Option 2: $\frac{4 \sqrt{2}-3 \sqrt{3}}{2}$ cm
Option 3: $\frac{4 \sqrt{2}-3 \sqrt{3}}{3}$ cm
Option 4: $\frac{4 \sqrt{2}-3 \sqrt{3}}{4}$ cm
Question : AB is the chord of a circle such that AB = 10 cm. If the diameter of the circle is 20 cm, then the angle subtended by the chord at the centre is?
Option 1: $45^{\circ}$
Option 2: $60^{\circ}$
Option 3: $30^{\circ}$
Option 4: $90^{\circ}$
Question : If $\sin\left ( 2a+45^{\circ} \right )=\cos\left ( 30^{\circ}-a \right )$ where $0^{\circ}< a< 90^{\circ}$, then the value of a is:
Option 1: $0^{\circ}$
Option 2: $15^{\circ}$
Option 3: $45^{\circ}$
Option 4: $60^{\circ}$
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