Respuesta :

Answer: Choice B) cos(69)

Work Shown:
cos(90-x) = sin(x)
cos(90-21) = sin(21)
cos(69) = sin(21)

Answer:

B. Cos 69°

Step-by-step explanation:

Given : sin 21°

Solution : To show how Cos 69 ° = Sin 21 °

we will use sine and cosine trigonometric identity

i.e. Cos (90 °-x) = Sin x           ---(A)

We are given Sin 21 °

So, putting x =21 ° in (A)

We are getting : Cos(90 °-21 °) = Sin 21 °

⇒Cos 69 ° = Sin 21 °

Hence it is shown that Cos 69 ° = Sin 21 °