How do you know weather two quantities x and y are proportional?
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Hi there!
The formula to find the are of a circle is :
a = r²
The formula to find the circumference of a circle is :
c = 2r
In order to use the area formula, you need to figure out what the radius (r) is.
If we solve for "r" in the circumference equation, we have :
r = c ÷ (2)
Now we use this to replace "r" in the area formula :
a = ( c ÷ (2
))²
When we simplify this we get :
a = c² ÷ 4
Now you can put your value of "c" into this equation and find "a".
*Remember, is about 3.1416.
Solving for "a" :
a = c² ÷ 4
a = 28² ÷ 4
28² = 28 × 28 = 784
a = 784 ÷ 4
4 = 4 ×
= 12.56637061435917
a = 784 ÷ 12.56637061435917
a = 62.38873769202297cm²
You need to round to the nearest square centimeter, which means that you need to round to the nearest whole number :
a = 62cm²
There you go! I really hope this helped, if there's anything just let me know! :)