9. Look at some of the printed letters in a textbook. The small horizontal
and vertical segments attached to the ends of the letters are called
serifs. Most of the letters in a textbook are in a serif typeface. The
letters on this page do not have serifs, so these letters are in a sans-
serif typeface. (Sans means "without" in French.) The figure shows a
capital letter A with serifs. Use the given information to write a
paragraph proof that the serif, segment HI, is parallel to segment JK.
Given: 21 and 23 are supplementary.
Prove: HI || JK