1. Let the m(YXZ)=a, m(XZY)=b, m(XYZ)=c, m(WXY)=d as in the atached figure.
A) d=a,
no, because clearly the triangle is an acute triangle (all angles clearly < 90°).
So a<90, and d, the supplementary of a, is >90. So d>a
B) d<b.
no, d >90, b<90 so d>b
C) d+a=180°
yes, because an interior angle, and that angles exterior angle are supplementary, that is, their sum is 180°
D) d+c=180°. True only if c=a, so if YZX is isosceles. Otherwise, not true.
