If cos x=8/17, and 270° < x < 360°
what is cos(2x)?

Step-by-step explanation:

Given: cos x = , x is in Quadrant 4

Use Pythagorean Theorem to find sin x:

8² + y² = 17²    

      y² = 17² - 8²

      y² = 289 - 64

      y² = 225

      y = 15

→    sin x =

Use the double angle formula to find cos (2x):

-

Step-by-step explanation:

Using the trigonometric identity

cos(2x) = 2cos²x - 1

given cosx = , then

cos(2x) = 2()² - 1

           = 2 × -

          = - = -

f(x) = - 2/3x + 5; f(5/2)

substitute 5/2 in for x:

f(5/2) = -2/3(5/2) + 5

simplify the right side:

f(5/2) = -5/3 + 5

f(5/2) = 10/3

answer:

f(5/2) = 10/3

i hope this you!