Question 57

The total surface area of a closed hemisphere is 4158 $$cm^{2}$$. What is the diameter of the hemisphere? [Use $$\pi = \frac{22}{7}$$]

Solution

total surface area of a closed hemisphere = $$3\times\ \pi\ \times\ \left(radius\right)^2$$

$$4158=3\times\ \frac{22}{7}\times\ \left(radius\right)^2$$

$$63=\frac{1}{7}\times\ \left(radius\right)^2$$

$$7\times\ 9\times\ 7\ =\ \left(radius\right)^2$$
$$\left(7\times\ 3\right)^2\ =\ \left(radius\right)^2$$

radius = 21 cm
diameter of the hemisphere = $$2\times radius$$
= $$2\times 21$$
= 42 cm

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