Question

Geometry help please!

Prove the Triangle Exterior Theorem.

The measure of each exterior angle of a triangle equals the sum of the measurements of its two remote interior angles.

Question in comments below.

Answer 1

m <1 + m < 4 = 180 degrees (angles on same line)
m<2 + m<3 + m<4 = 180 ( 3 angles of triangle add up to 180 degrees)

since m < 1 plus m<4 = 180
and m<2 + m<3 plus m< 4 is also = 180 degrees

m<1 = m <2 + m < 3

Answer 2

Awesome! Thank you for explaining it :)

Answer 3

yw - that is how i was taught in UK - the US method might use different terms.