Question

Find the exact value of the trigonometric function at the given real number.
1. cos (-13pi/20)

2. cos (10pi/3)

Answer 1

for the first one i got \[-\sqrt{3}/2\]

Answer 2

second one: 10pi/3 = 9pi/3 + pi/3 = 3pi + pi/3 = -cos(pi/3) = -1/2

Answer 3

for the first one:

-13pi/20 = -(10pi/20 + 3pi/20) = -pi/2 - 3pi/20

cos(-pi/2 - 3pi/20) = -sin(3pi/20)

The exact value is -sin(3pi/20)

Answer 4

well.. I just found out another exact value for the first equation:

\[(-1/2)\sqrt{(1/2) (4-\sqrt{2(5-\sqrt{5}}))}\]

Answer 5

I type in the first one wrong

Answer 6

cos (-13pi/6)

Answer 7

but following your steps should help me find the answer

Answer 8

thats easy then.

-13pi/6 = -12pi/6 -pi/6 = -2pi -pi/6

cos(-2pi -pi/6) = cos(-pi/6) = sqrt(3)/2

Answer 9

Find the exact value of the trigonometric function at the given real number. Csc7pi/3

Answer 10

Can someone help me on this question above