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Find the radius of a hemisphere with a volume of 80 cm³.

(Note: The volume, [tex]\( V \)[/tex], of a sphere with radius [tex]\( r \)[/tex] is [tex]\( V = \frac{4}{3} \pi r^3 \)[/tex].)


Sagot :

To find the radius of a hemisphere with a volume of [tex]\(80 \, \text{cm}^3\)[/tex], we need to follow a series of steps involving the formula for the volume of a sphere. Here is the detailed, step-by-step solution:

1. Volume Relationship Between Hemisphere and Sphere:
The volume [tex]\(V_{\text{hemisphere}}\)[/tex] of a hemisphere is half of the volume [tex]\(V_{\text{sphere}}\)[/tex] of a full sphere. Given the volume of the hemisphere is [tex]\(80 \, \text{cm}^3\)[/tex]:
[tex]\[ V_{\text{sphere}} = 2 \times V_{\text{hemisphere}} \][/tex]
Substituting the given volume:
[tex]\[ V_{\text{sphere}} = 2 \times 80 \, \text{cm}^3 = 160 \, \text{cm}^3 \][/tex]

2. Formula for the Volume of a Sphere:
The volume of a sphere is given by the formula:
[tex]\[ V = \frac{4}{3} \pi r^3 \][/tex]
where [tex]\(r\)[/tex] is the radius of the sphere. Given the volume [tex]\(V_{\text{sphere}} = 160 \, \text{cm}^3\)[/tex], we can set up the equation:
[tex]\[ 160 = \frac{4}{3} \pi r^3 \][/tex]

3. Solving for the Radius:
We need to solve for [tex]\(r\)[/tex]. Start by isolating [tex]\(r^3\)[/tex]. Multiply both sides of the equation by [tex]\(\frac{3}{4 \pi}\)[/tex]:
[tex]\[ r^3 = 160 \times \frac{3}{4 \pi} = \frac{480}{4 \pi} = \frac{120}{\pi} \][/tex]

4. Cube Root to Find the Radius:
To find [tex]\(r\)[/tex], we need to take the cube root of [tex]\(\frac{120}{\pi}\)[/tex]:
[tex]\[ r = \sqrt[3]{\frac{120}{\pi}} \][/tex]

5. Simplification and Numerical Solution:
Evaluating the above expression numerically, we find:
[tex]\[ r \approx 3.367 \, \text{cm} \][/tex]

So, the radius of the hemisphere is approximately [tex]\(3.367 \, \text{cm}\)[/tex].