Hey there, Guest!
It appears that the question that you asked has already been answered here: https://web2.0calc.com/questions/more-hw-please-help.
In case if you're one of the people online of which don't like links, this is what it says:
In triangle PQR, PQ=13, QR=14, and PR=15. Let M be the midpoint of QR. Find PM.
Let angle PRQ be >β<
1) Let's find β first: cos(β) = (15² + 14² - 13²) / 2*15*14 β = 53.13°
2) Now we can find PM (PM)² = 7² + 15² - 2*7*15 * cos(β)
PM = 12.166
Answerer: Dragan
Hope this helped! :)
( ゚д゚)つ Bye