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What is the volume of a pyramid with a regular pentagonal base of side 6 cm and a height of 10 cm?

Mathematics

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Step-by-step solution

2 steps
  1. Find the volume of the pyramid.

    The formula for the volume of a pyramid is given as V=13AhV = \frac{1}{3}Ah, where AA is the area of the base and hh is the height.
    From the image:

    • The base is a regular pentagon with a side length (ss) of 6 cm6 \text{ cm}.
    • The height (hh) of the pyramid is 10 cm10 \text{ cm}.

    First, calculate the area of the regular pentagonal base (AA). The formula for the area of a regular pentagon with side length ss is:

    A=5s24tan⁡(180∘5)=5s24tan⁡(36∘)A = \frac{5s^2}{4\tan(\frac{180^\circ}{5})} = \frac{5s^2}{4\tan(36^\circ)}

    Substitute s=6 cms = 6 \text{ cm}:

    A=5×(6 cm)24tan⁡(36∘)A = \frac{5 \times (6 \text{ cm})^2}{4\tan(36^\circ)} A=5×36 cm24tan⁡(36∘)A = \frac{5 \times 36 \text{ cm}^2}{4\tan(36^\circ)} A=180 cm24tan⁡(36∘)A = \frac{180 \text{ cm}^2}{4\tan(36^\circ)} A=45tan⁡(36∘) cm2A = \frac{45}{\tan(36^\circ)} \text{ cm}^2

    Using tan⁡(36∘)≈0.72654\tan(36^\circ) \approx 0.72654:

    A≈450.72654 cm2≈61.937 cm2A \approx \frac{45}{0.72654} \text{ cm}^2 \approx 61.937 \text{ cm}^2

    Now, calculate the volume (VV) of the pyramid:

    V=13AhV = \frac{1}{3}Ah

    Substitute the calculated area and the given height:

    V=13×(45tan⁡(36∘)) cm2×10 cmV = \frac{1}{3} \times \left(\frac{45}{\tan(36^\circ)}\right) \text{ cm}^2 \times 10 \text{ cm} V=150tan⁡(36∘) cm3V = \frac{150}{\tan(36^\circ)} \text{ cm}^3

    Using the approximate value for tan⁡(36∘)\tan(36^\circ):

    V≈1500.72654 cm3V \approx \frac{150}{0.72654} \text{ cm}^3 V≈206.457 cm3V \approx 206.457 \text{ cm}^3

    Rounding to two decimal places:

    206.46 cm3\boxed{206.46 \text{ cm}^3}
  2. Find the volume of the sphere.

    The formula for the volume of a sphere is given as V=43πr3V = \frac{4}{3}\pi r^3.
    From the image:

    • The radius (rr) is 60 mm60 \text{ mm}.
    • Use π=3.14\pi = 3.14.
    • The answer should be given to the nearest cubic centimetre.

    First, convert the radius from millimeters to centimeters:

    r=60 mm=6 cmr = 60 \text{ mm} = 6 \text{ cm}

    Now, substitute the values into the volume formula:

    V=43×3.14×(6 cm)3V = \frac{4}{3} \times 3.14 \times (6 \text{ cm})^3 V=43×3.14×(6×6×6) cm3V = \frac{4}{3} \times 3.14 \times (6 \times 6 \times 6) \text{ cm}^3 V=43×3.14×216 cm3V = \frac{4}{3} \times 3.14 \times 216 \text{ cm}^3 V=4×3.14×2163 cm3V = 4 \times 3.14 \times \frac{216}{3} \text{ cm}^3 V=4×3.14×72 cm3V = 4 \times 3.14 \times 72 \text{ cm}^3 V=12.56×72 cm3V = 12.56 \times 72 \text{ cm}^3 V=904.32 cm3V = 904.32 \text{ cm}^3

    Rounding to the nearest cubic centimetre:

    904 cm3\boxed{904 \text{ cm}^3}
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