posted by zoya .
a diagram shows a cross section of a triangular prism.
m is the midpoint of the line segment AC.
a) explain why angle AMB must be a right angle.
b) calculate angle BCM.
c) calculate area of the triangle
ABC is an isosceles triangle, so the altitude BM intersects AC in the middle.
cos BCM = 5/7
area = 1/2 AC * BM