# Cos Theta Formula

Amongst all the trigonometric formulas, the most important ones are the right triangle formulas. The Cos Θ = Adjacent / Hypotenuse

## Cos angle formula / Cos phi formula

There are many formulas in trigonometry but there are few most important basic formulas in trigonometry when it comes to right angle triangle. The Cos Θ is the ratio of the adjacent side to the hypotenuse, where (Θ is one of the acute angles. The cosine formula is as follows:

 $Cos \Theta = \frac{Adjacent}{Hypotenuse}$

## Cos x Questions

Example 1:

If Sin x = 4/5, Find the value of Cos x?

Solution: Using Trigonometric identities: Cos2x = 1- Sin2x

Cos2x = 1 – (4/5)2

= 1 – 16/25

= (25 – 16) / 25

= 9/25

Cos x = $\sqrt{9/25}$

= 3/5

Example 2: If Sec x = 4/7, find the Cos x?

Solution: As Cosec x = 1/sin x

= 1/ 4/7

= 7/4

## Practice questions on cos formula trigonometry

Q1) Find cos x, if sin x =25

Q2) Find Cos a, If Sin a = 37