Answer:
C) 
Step-by-step explanation:
By the cos double angle formula, we know 
Substituting 
into the formula, we get
.
The answer is C.
Answer:
0.16
Step-by-step explanation:
Note that the formula for the circumference of a circle is πd, while the formula for the area of a circle is πr².
π≈3.14
A. C=πd
Simply plug in the numbers into the formula.
Diameter=Radius*2
17*2=34
C=34(π)
B. (π)(5²)
Plug in the numbers into the formula. Remember that half of the diameter is the radius.
C. (π)(4.5)
There are two possible formulas that could be used to calculate the circumference of a circle: πd and 2πr.
The expression above is simply multiplying the circle's radius times pi. Therefore, it is not a method that could be used to find the circumference of a circle.
D. (π)(6.5²)
Remember that the formula for calculating the area of a circle is πr².
Half of the diameter is 6.5 (13.5/2=6.5). 6.5 cm. is the radius. Now just plug the numbers into the formula.
(π)(6.5²)
Therefore, the last answer choice is the correct answer.
