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 × -

          = - = -

it 2

step-by-step explanation:

8^1/3=2