F=[ 0
5


4
2

] and \text D = \left[\begin{array}{rr}2 & 5 \\ 3 & 0\end{array}\right]D=[
2
3


5
0

].
Let \text {H = FD}H = FDstart text, H, space, =, space, F, D, end text. Find \text HHstart text, H, end text.

1. 180°. the sum of the interior angles of a triangle is 180°, for the equilateral triangle that it has three equals side is 60°+60°+60°=180°.

2. 60°. each interior angle of a equilateral triangle is 60°

3. 120°. the measure of ∠m is 120°, the sum of the angles ∠m and ∠n is equal to 180°. so, in order to find the measure of ∠m, we have ∠m+∠n=180° > ∠m=180°-∠n > ∠m=180°-60°=120°.

4. 360°. the sum of the exterior angles of an equilateral triangle is ∠m+∠r+∠x=120°+120°+120°=360°. the exterior angles of any triangle always add 360°.