Question

show that angle 1 plus angle 2 subtract angle 3 is equal to 180
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Answer 1

Given: l || m

RTP : angle 1 + angle 2 - angle 3 = 180 degree

Construction: Extend BC and let it intersect line 'm' at point 'F'. Let the angle BFD be 4.

proof: now,

         angle 1 +angle  4 = 180 degree (co-int pair)

         or angle 4= 180 - angle 1 -----(1)

IN triangle BCF ,

 angle 3 + angle 4 = angle 2 (Exterior angle )

Applying equation 1, we have

angle 3 + 180- angle 1 =angle 2

or angle 1 + angle 2 -angle 3 = 180 (proved)