If a+b+c=pi show that cos a/2+cos b/2 cos c/2= 4cos (b+c/4)cos (c+a/4)cos(a+b/4)

Geometry: determine whether segment mn is parallel to segment kl. justify your answer. jm 6 mk 3 jn 8 nl 4

Expresa commuter train leaves downtown sation and travels at a average speed of 55 miles per hour towards the north side sation, which is 50miles away. thirty minutes later, express commuter train #7 leaves north side and travels at a average speed of 35miles per hour towards downtown sation. at the moment the two trains pass each other, how far(in miles) is train #12 from the downtown sation and how long(in minutes) has the #12 train been traveling

How many sides does a regular polygon have if each exterior angle measure is 45 degrees explain your answer, i really don't understand this.