now let's recall that a full circle has 360°, so then 1140 = 360 + 360 + 360 + 60.
namely, 1140 is 3 full-go-around the circle and then it lands on the I Quadrant at 60°. Thus cos(1140°) = cos(60°).
what's that cosine of 60°? Check the picture below.
Answer:
Grace should use her phone for 58 minutes to maintain an average of 55 minutes.
Step-by-step explanation:
Usage of first month = 43 minutes
Second month = 62 minutes
Third Minutes = 57 minutes
Let, the usage of fourth month = k minutes
Mean of the data = 5 minutes
Now, Average of a Data =
⇒
or, 55 x 4 = 162 + k
⇒ 220 - 162 = k
or, k = 58 minutes
So, Grace should use her phone for 58 minutes to maintain an average of 55 minutes.