Before you can accurately draw triangles, you need to know the kinds of angles they embody. Right angles are 90-degree angles that form a perfectly square corner. Acute angles are less than 90 degrees. Obtuse angles are greater than 90 degrees, but less than 180 degrees. A straight angle, or what we normally think of as a straight line, travels on a 180 degree plane. A reflex angle, which is never part of a triangle's interior, is greater than 180 degrees.
Every triangle has three arms, which are the three straight lines of the sides. Any corner, or angle, where two arms meet at a point is a vertex. The size of the angle is measured in degrees. If you were to add the degrees of all three angles in a triangle, no matter how big or small it is, they will always add up to 180 degrees.
You can label each vertex with a letter, such as A, B and C. Then you can refer to each angle by three letters -- the letters of the two vertices at the end of either of its sides with the letter of the vertex in the middle. So the vertex, or angle, you have labeled A is properly called angle BAC.This is because one arm of the angle stretches from vertex B to vertex A, and another arm stretches from vertex C to vertex A.
Just as there are different types of angles, there are different types of triangles. A right triangle will always have one 90-degree angle. An acute triangle will always have one angle that is less than 90 degrees. And an obtuse triangle will always have one angle that is more than 90 degrees. But remember that no matter what, if you add all three angles of one triangle together, they will always total 180 degrees.
Triangles will also have arms of different lengths. Sometimes they are all the same length, or sometimes two of the arms are the same length, but the third arm is a different length. And sometimes all three arms are different lengths.
When all three arms are different lengths, you have a scalene triangle. Scalene triangles also have three different size angles. When two arms are the same and only one is different, you have an isosceles triangle. An isosceles triangle will also have two angles that are the same size and one that is different. An equilateral triangle always has three arms of the same length and three angles that are all the same size.
Sometimes names are combined. A right isosceles triangle, for example, will have one right angle and two other angles that are equal to each other. The other two angles will always equal 45 degrees.
To draw triangles accurately, you need graph paper, a straight edge and a protractor, which is a device for measuring angles in degrees.
Start by marking a dot on a piece of graph paper. Then lay your protractor flat on the graph paper so that the zero line rests on the dot, with the dot at the line's middle point. Next, if you want to draw a right triangle, for example, locate the 90 degree mark on your protractor and mark a dot at its location on the paper. Be careful not to move or wiggle the protractor from its original position. Now mark a dot at the zero line on the side of the protractor. You now have three dots on the paper. Use your straight edge to draw the arms of the triangle from dot to dot.
Always begin with three dots, marking the second dot at the number of degrees that you desire and the third dot at the zero line at the side.