On the third week of math 10 we got into trigonometry.
We went through triangles and ratios. We’ve learned the names of the triangle’s sides like hypotenuse, opposite and adjacent. We call side opposite when it is in front of the delta angle. And as you can see on the picture, we call side adjacent when it is right next to the delta angle.
To find sine of the angle you need to divide opposite side by hypotenuse. To find cosine of the angle you need to divide adjacent by hypotenuse. And to find tangent you need to divide opposite side by adjacent.
If we will look on the example, then we will see that angle B is the one we are searching for. We see that in front of the angle B there is side AC that is our opposite side. The biggest side next to 
angle B is hypotenuse and another one next to B is adjacent. So, to find sine, cosine, and tangent we need to use our formula.