Question : The base of a right pyramid is an equilateral triangle, each side of which is 20 cm. Each slant edge is 30 cm. The vertical height (in cm) of the pyramid is:
Option 1: $10 \sqrt{\frac{23}{3}}$
Option 2: $5 \sqrt{3}$
Option 3: $10 \sqrt{3}$
Option 4: $5 \sqrt{\frac{23}{3}}$
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Correct Answer: $10 \sqrt{\frac{23}{3}}$
Solution : The base of the right pyramid is an equilateral triangle, each side, (a) = 20 cm Each slant edge, (E) = 30 cm According to the question Each side of an equilateral triangle = 20 cm We know that, circumradius of the equilateral triangle = $\frac{a}{\sqrt{3}}$ ⇒ AD = $\frac{20}{\sqrt{3}}$ h = $\sqrt{(AE^2 – AD^2)}$ h = $\sqrt{30^2 – (\frac{20}{\sqrt{3}})^2}$ ⇒ h = $\sqrt{900 – (\frac{400}{3})}$ ⇒ h = $\sqrt{\frac{2700-400}{3}}$ ⇒ h = $\sqrt{\frac{2300}{3}}$ ⇒ h = $10\sqrt{\frac{23}{3}}$ $\therefore$ The vertical height of the pyramid is $10\sqrt{\frac{23}{3}}$cm. Hence, the correct answer is $10\sqrt{\frac{23}{3}}$cm.
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Question : The base of a right pyramid is an equilateral triangle with a side of 8 cm, and its height is $30 \sqrt{3}$ cm. The volume (in cm$^3$ ) of the pyramid is:
Option 1: $240 \sqrt{3}$
Option 2: $360 \sqrt{3}$
Option 3: $480$
Option 4: $360$
Question : A pyramid has an equilateral triangle as its base, of which each side is 8 cm. Its slant edge is 24 cm. The whole surface area of the pyramid (in cm2) is:
Option 1: $(16 \sqrt{3}+24 \sqrt{35})$
Option 2: $(12 \sqrt{3}+24 \sqrt{35})$
Option 3: $(24\sqrt{3}+36\sqrt{35})$
Option 4: $(16\sqrt{3}+48\sqrt{35})$
Question : The base of a right pyramid is a square of side $8 \sqrt{2}$ cm and each of its slant edges is of length 10 cm. What is the volume (in cm$^3$) of the pyramid?
Option 1: $256$
Option 2: $224$
Option 3: $426 \frac{2}{3}$
Option 4: $96 \sqrt{2}$
Question : $\triangle PQR$ is right-angled at $Q$. The length of $PQ$ is 5 cm and $\angle P R Q=30^{\circ}$. Determine the length of the side $QR$.
Option 1: $5 \sqrt{3}~cm$
Option 2: $3 \sqrt{3}~cm$
Option 3: $\frac{1}{\sqrt{3}}~cm$
Option 4: $\frac{5}{\sqrt{3}}~cm$
Question : The side of an equilateral triangle is 9 cm. What is the radius of the circle circumscribing this equilateral triangle?
Option 1: $2\sqrt{3}$ cm
Option 2: $5\sqrt{3}$ cm
Option 3: $4\sqrt{3}$ cm
Option 4: $3\sqrt{3}$ cm
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