 Triangles come up a lot in maths, and the study of them is known as trigonometry. One reason is that they are the building blocks of all other straight-edge shapes. They were used for hundreds of years to create accurate maps, and GPS today still works using trigonometry. Even the pixels on phones and screens use trigonometry. So we have to learn quite a bit about triangles under the topic of trigonometry. In this video, we're going to learn about the names of the sides of a right angle triangle and also the three special trig functions. We need to know these things so that we can work out exact lengths of sides of triangles or how big set of angles are in triangles. There are three main functions in trigonometry, sine, cosine and tangent, but we just call them sine, cosine and tan, which is how they are labelled on your calculator. These functions are just ratios between sides and angles on right angle triangles. So we need to firstly know which side is the hypotenuse, which is the opposite, and which is the adjacent. The hypotenuse is the longest side and is opposite the right angle. Then we have the adjacent and the opposite. These change positions depending upon which angle we are using. Here, this side is the opposite because it is opposite the angle, and this side is the adjacent because it is next to the angle. But see how when we change the angle, the adjacent and the opposite move. So is this side the adjacent, the hypotenuse or the opposite? It's the opposite because it is opposite the angle. What about this side? It's the hypotenuse because it's the longest side and it's across from the right angle. So now we know about the adjacent opposite and hypotenuse, we're ready to learn about the special thing called sockatoa. So sine, cosine and tan are just ratios between sides and angles on right angle triangles. Sockatoa helps us remember which function to use to find which sides. S is for sine, C is for cos, T is for tan, O is for opposites, H is for hypotenuse and A is for adjacent. We will learn how to use sockatoa in the videos on finding missing sides and finding missing angles, but for now you just need to remember the word. So from this video you should be able to label the sides the adjacent, opposite and hypotenuse on a right angle triangle and you should remember the word sockatoa and that it represents sine, cos and tan.