In triangle PQR, M is the midpoint of ¯QR. Find PM.
Law of Cosines
[ 23^2 - 25^2 -18^2] / [ -2 * 25 * 18 ] = cos (angle Q) = 7/15
Once more → QM = 12.5
PM = sqrt [18^2 + 12.5^2 - 2 [ 18 * 12.5] * [ 7/15] ] ≈ 16.44
