Given the point on the coordinate plane , the origin to this point can be computed by the Pythagorean Theorem.

The hypotenuse of the right triangle formed by the origin and the point is .

The length of the triangle is 1 unit, and the height of the triangle is 5.

Sine of an angle is opposite side divided by the hypotenuse.

Rationalize the denominator.

First, use the Pythagorean Theorem to solve for all the sides of the triangle. You know that the adjacent side is 4 units long, and the opposite side is -9 units long.

Using the Pythagorean Theorem, you should get a hypotenuse of .

Secant is defined as hypotenuse/opposite.

Thus, giving you an answer of .

This is a 30-60-90 triangle. A 30-60-90 triangle will have leg lengths of  and 1 and a hypotenuse of 2. To find the sin value, you need to divide the opposite leg length with the hypotenuse (opposite/hypotenuse). Thus, giving you .

Recall the formula for tangent is .  If we have enough information to solve for sine and cosine, then we have the values of the opposite and adjacent of the angle.

Consider the figure below.

We can form a triangle by dropping a line down from the point (-2,3) perpendicular to the 

x axis.  Now we have right triangle that has a leg that is 3 units high and a base that is 2 

units long.  Now we can use the Pythagorean Theorem to solve for the hypotenuse.

We can solve for sine and cosine now.  Use the fact that .  The opposite side of the angle in this case is the leg that is 3 units high.

And we will use the fact that .  The adjacent side to the angle is the base that is 2 units long.  We do have to note that we are using and not .

So even though our angle was obtuse, we can still use the same method.

We begin by thinking about what cosine means when working with right triangles.  Recall .  So if

Then the adjacent side, or the base of the triangle, is 1 and the hypotenuse is 2.  Now we can use the Pythagorean Theorem to solve for the missing side. 

Using the point (3,4), we can see that this forms a right triangle that has a base that is 3 units in length and an adjoining leg that is 4 units high.  We are able to find the hypotenuse of this triangle using the Pythagorean Theorem.  This will give us the distance of the point (3,4) to the origin. 

And so the hypotenuse of this triangle (the distance from our point we are working with to the origin), is 5 units long.  Recall that when using cosine for right triangles, cosine represents the following

So if we are considering the angle formed by the x-axis and our hypotenuse, the adjacent side would be the base of our triangle; 3 units. 

We see that the point on the terminal side is (5,6).  So we know that with this point a right triangle is formed with a base that is 5 units long, and a leg that is 6 units high.  We can use the Pythagorean Theorem to solve for the hypotenuse that is formed by this triangle and this will tell us the distance of the point from the origin. 

Let’s solve for sine first.  When working with right triangles recall that and we are considering the angle formed by the x-axis and the hypotenuse.  So the opposite side is the leg that is 6 units high.

We can solve for cosine if we recall that .  Our adjacent side would be the base that is 5 units long.