# Thread: Show Euclid's Fifth implies Playfair's Postulate

1. ## Show Euclid's Fifth implies Playfair's Postulate

Can someone help with this? I'm not sure how to show m(angle)DAB + m(angle)ABC is less then 180 degrees. Then to apply Euclid Fifth so t intersects m. Then show t can't intersect m on the "wrong side". Thus t doesn't parallel m and Playfair's postulate holds. See figure.

Any help would be greatly appreciated...

2. Originally Posted by mdk
Can someone help with this? I'm not sure how to show m(angle)DAB + m(angle)ABC is less then 180 degrees. Then to apply Euclid Fifth so t intersects m. Then show t can't intersect m on the "wrong side". Thus t doesn't parallel m and Playfair's postulate holds. See figure.

Any help would be greatly appreciated...
I'm not clear why you say 'Then show t can't intersect m on the "wrong side" ' Once you have shown that "t intersects m" you are done.

3. Do you mean you want to prove Post. 5?