Answer:
7. A = π
8. A = 6.25π
9. A = 16π
Step-by-step explanation:
When you have a bunch of similar problems that all use the same formula, it is usually convenient to solve the problem in generic terms, then put in the specific numbers.
You are asked to find A, and you are given the formula ...
[tex]C^2=4\pi A[/tex]
To rewrite this as an equation for A, you divide by its coefficient, 4π.
[tex]A=\dfrac{C^2}{4\pi}[/tex]
If you like, you can go one step further, replacing C with kπ. Now, you have ...
[tex]A=\dfrac{(k\pi)^2}{4\pi}=\dfrac{k^2}{4}\pi[/tex]
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7. k=2, A=(2^2)/4·π
A = π
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8. k=5, A=(5^2)/4·π
A = (25/4)π
A = 6.25π
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9. k=8, A=(8^2)/4·π
A = 16π
