This is an isosceles right triangle (AB = BC & ∠ B=90° - Given) Then the angles at the base are equal and ∠ CAB = ∠ ACB = 45°
Theorem: Segment DE, joining the midpoints of 2 sides is: 1st) parallel to the 3rd side and 2nd) equal to half the measurement of the 3rd side So if the 3rd side (hypotenuse) = 9 units, DE = 9/2 = 4.5 units
