You could use a compass and measure out th e leng the length of the base by spreading the sharp edge of the compass at one end of the length and the pencil side at the other create a line this long. then since you already have the measured length of 7 on your compass place the sharp point of it on one end of the already formed line and make a half circle, then measure out 5 units with your compass and do the some thing with the other end of the line. there should be a crossing point where you made the arcs, if not remake the arcs into a full circle just to make sure. where they crossed create a point and draw a line connecting all edges, I really hope this helped.
