# Trigonometry

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a diagram shows a cross section of a triangular prism.
AB=BC=7cm. BM=5cm
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

• Trigonometry -

ABC is an isosceles triangle, so the altitude BM intersects AC in the middle.

cos BCM = 5/7

area = 1/2 AC * BM

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