In this page we practice using the rule:
Sum of interior angles of a triangle \(= 180^\circ\)
Example 1
Angles of a triangle are:
\(40^\circ, 60^\circ,\) and \(x\).
$$40^\circ + 60^\circ + x = 180^\circ$$
$$100^\circ + x = 180^\circ$$
$$x = 80^\circ$$
Example 2
Angles of a triangle are:
\(90^\circ, 35^\circ,\) and \(x\).
$$90^\circ + 35^\circ + x = 180^\circ$$
$$125^\circ + x = 180^\circ$$
$$x = 55^\circ$$
Example 3
Two angles of a triangle are equal and one angle is \(40^\circ\).
Let the equal angles be \(x\).
$$x + x + 40^\circ = 180^\circ$$
$$2x + 40^\circ = 180^\circ$$
$$2x = 140^\circ$$
$$x = 70^\circ$$
So the triangle has angles:
\(70^\circ, 70^\circ,\) and \(40^\circ.\)
Example 4
Angles of a triangle are:
\(x, x,\) and \(x\).
$$x + x + x = 180^\circ$$
$$3x = 180^\circ$$
$$x = 60^\circ$$
So all angles are \(60^\circ\).
Example 5
Angles of a triangle are:
\(80^\circ, 70^\circ,\) and \(x\).
$$80^\circ + 70^\circ + x = 180^\circ$$
$$150^\circ + x = 180^\circ$$
$$x = 30^\circ$$
Practice
- More Examples (Current page)
- Take the Quiz