8th Grade - Trigonometry

8th Grade lesson

9 - Trigonometry

Formulas of cosine, sine and tangent

Learn this trick :
learn trigonometry formulas

By grouping letters 3 by 3 (two on the top and one below), it permits to keep in mind these 3 formulas which are very useful :
sine formula cosine formula tangent formula

For you who knows well the cosine, this part of the site is easy : it is exactly the same thing except that there are two more formulas. Here are two examples to practice.

Using trigonometry formulas

Calculate CI.
calculs dans un triangle

Since we already know one angle, we have the opposite edge and we are looking for the adjacent edge, so we need the formula of the tangent.
tangent use

And here comes the other example :

Calculate the angle angle calculation.
angle calculation

To find the angle we are looking for, we have the opposite edge and the hypothenuse, so it is the formula of the sine that we need.

Be careful with the last but one step which is done with the calculator, teachers do not like you to write on the sheet because the sign (-1) has nothing to do with powers.

See also : trigonometry on

>>> Lesson on vectors >>>


lesson, problems