Question

Given cosΘ=2/3 and sinΘ>0, find sinΘ

(Just for clarification, those zeros with horizontal lines in the center represent theta)

Answer 1

sinΘ = √5/3

Explanation:

Mathematically, we know that the cos of an angle is the ratio of the adjacent to the hypotenuse

The sine of an angle is the ratio of the opposite to the hypotenuse

So in this case, from the cosine given; adjacent is 2 and hypotenuse is 3

From the Pythagoras’ theorem, we can get the opposite

Mathematically, the square of the hypotenuse equals the sum of the squares of the two other sides

Let us have the opposite as x

3^2 = 2^2 + x^2

9 = 4 + x^2

x^2 = 9-4

x^2 = 5

x = √5

This root can be positive or negative

But since the sine is positive, we shall be considering only the positive root

Thus;

sine theta = √5/3