Question

The function f(t) = 4 cos(pi over 3t) + 15 represents the tide in Bright Sea. It has a maximum of 19 feet when time (t) is 0 and a minimum of 11 feet. The sea repeats this cycle every 6 hours. After five hours, how high is the tide?
13.5 feet

16 feet

18.5 feet

17 feet

Answer 1

you need to find the value of cos(5pi/3)

in degrees that is 5*180/3 = 5*60 = 300º

300º is in the 4th quadrant.
it will be the same value as cos(60º)

Answer 2

\[ f(5) = 4\cos\left( \frac{\pi}{3} \cdot 5 \right)+15 \]

Answer 3

sorry my open study is messing up right now

Answer 4

omg my calculator just died.. can u plug that in and see what u get?

Answer 5

first, people memorize the sin, cos and tan of certain angles: 0,30,45,60 and 90
so you should know 60º

second, type it into the google search window (but google uses radians)

Answer 6

i got 16 feet

Answer 7

what did you get for the cos part?

Answer 8

16

Answer 9

cos is between -1 and 1

what is cos(5 pi/3) ?

Answer 10

its not working

Answer 11

type into google
cos(5 pi/3)=

Answer 12

.5

Answer 13

now do
f(5)= 4*0.5 + 15

Answer 14

17

Answer 15

yes

Answer 16

thank u