Cosine law
a^2 = b^2 + c^2 - 2(b)(c)cosA
a^2 = 2^2 + 4^2 - 2(2)(4)cos78
a = 4.08
a = 4.1
Answer:
27. C
28. D
Step-by-step explanation:
The average of all grades in his fencing class, including the upcoming one, (all grades summed up divided by the amount of grades) must be equal to 86 (percent), hence C is the right answer for 27.
Solving this equation gives:

So D is the right answer for 28.
1/4 x 24 is 6.
Your welcome
The circumference of a circle is equal to C=2πr
From the question, we have 615.44.
Assume that pi is equal to 3.14
Substitute and solve for r
615.44= 2(3.14)r
r= 615.44/ 6.28
r=98.4704
r=98
Therefore, the radius is about 98 units.
To check:
C=2πr
C=2 x 3.14 x 98
C=6.28 x98
C=615.44