Complementary and supplementary angles.

Two angles are complementary if they add up to 90º, i.e. a right angle.

Two angles are supplementary if they add up to 180º, i.e. a straight angle.

8. Work out the complementary and supplementary angles of the following angles:

a.     56º 20' 40"

b.     37º 42' 15"

c.     25º 50' 40"

d.     33º 33' 33"

e.     17º 43' 34"

Check your results in the following window.

deg, min and sec correspond to the parts of the first angle measurements, indicated in red.

The three interior angles of any triangle add up to 180º. One of the angles in a right-angled triangle is a right angle. Therefore, the other two acute angles in any right-angled triangle add up to 90º, in other words they are complementary.

9. Move point A around the circumference in the following window. The triangle ABC is always a right-angled one, whatever the position of A. Construct triangles in the shape of two set squares (one is a right-angled triangle whose other angles are 60º and 30º and the other is an isosceles triangle whose acute angles both measure 45º).

Use the mouse to drag the red point.