You will need
  • Table of sines and cosines, table Bradis
Denote the angles of a triangle with the letters a, B, and C, as shown in the figure. The angle BAC is 90º, the other two corners will be denoted by letters α and β. The legs of the triangle will be denoted by the letters a and b and the hypotenuse c.
In this figure, all the notations that will be used in the article
Then sinα = b/c, cosα = a/c.

Similarly, the second acute angle of the triangle: sinβ = a/c, cosβ = b/c.

Depending on which sides are known to us, calculated the sines or cosines of angles and look at the table Bradis the value of α and β.
Finding one of the corners, you may recall that the sum of the internal angles of a triangle equal to 180º. Thus the sum of α and β equal to 180º - 90º = 90º.

Then, by calculating a value for α according to the table, unable to find β to use the following formula: β = 90 ° - α
If one of the unknown sides of a triangle, use the Pythagorean theorem: a2+b2=c2. Derive from it the expression for the unknown side using the other two and substitute into the formula for finding the sine or cosine of one of the corners.