If cos x = 2 / 3 and x is in quadrant 4, find:

a. sin(x / 2)

b. cos(x / 2)

c. tan(x / 2)

A

Step-by-step explanation:

cos(x)=2/3 in Q 4

sin(x/2)=+√(1-cos(x))/2

√(1-cos(x))/2=√(1-[2/3]/2=√(1/3)/2=-√(1/6) because sin is negative in Q 4

See below.

Step-by-step explanation:

Because cos x = 2/3 the adjacent side = 2 and hypotenuse = 3 so the length of the opposite side =  

√(3^2 - 2^2) =  -√5 (its negative because we are in Quadrant 4).

So sin x =  -√5/3.

(a) sin (x /2) =  - √ [ (1 - cos x)/2 ]

= -√(1 - 2/3)/ 2)

= -√(1/6).  or -0.4082.

(b)  cos (x/2)  = √ [ (1 + cos x)/2]

=  √ 5/6 or 0.9129.

(c)   tan (x /2) =   ( 1 - cos x) / sin x.

=  ( 1 - 2/3) /   -√5/3

= -0.4472.

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