A two-column proof incorrectly proving that the three angles of ΔPQR add up to 180°
- Line YZ should be drawn parallel to PQ
YZ is drawn parallel to PQ through the point R
<ZRP + <PRQ + <QRY = <ZRY
<ZRP = <RPQ [YZ // PQ]
<QRY = <PQR [YZ // PQ]
From the above,
<PQR + <RPQ + <PRQ = <ZRY =
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