Video Transcript
Find the measure of angle
𝐴𝐵𝐶.
In the diagram, we have a
triangle. We’re given the angle 𝐶𝐴𝐵 as 58
degrees. And we need to work out this angle
of 𝐴𝐵𝐶. We should notice that on this
diagram, we have two hash markings on the lines, indicating that there’s two equal
sides. So we could say that triangle
𝐴𝐵𝐶 is in fact an isosceles triangle, as an isosceles triangle is defined as a
triangle that has two sides equal in length.
An important property of isosceles
triangles is that base angles are equal. In an isosceles triangle, the
unequal side is referred to as the base, so that would be this line 𝐴𝐵. And the base angles would be the
two angles adjacent to this base. But be careful because the base
isn’t always at the bottom of the diagram.
We can therefore write that angle
𝐴𝐵𝐶 is equal to angle 𝐵𝐴𝐶. As we’re given that angle 𝐵𝐴𝐶 is
58 degrees, then so is angle 𝐴𝐵𝐶. We can give our answer then that
the measure of angle 𝐴𝐵𝐶 is 58 degrees.
