In triangle $PQR,$ $M$ is the midpoint of $\overline{QR}.$ Find $PM.$
[PR^2 - QR^2 - PQ^2 ] / [- 2 (QR * PQ] = cos PQR
[23^2 -25^2 - 18^2 ] / [ -2 (25 * 18) ] = cos PQR = 7/15
PM^2 = QM^2 + QP^2 - 2 (QM * QP) * cos PQR
PM^2 = 12.5^2 + 18^2 - 2(12.5 * 18)* (7/15)
PM = sqrt (270.25) ≈ 16.44
+1533 
