In trapezoid CDEF, angle D = angle E=90degrees. Angle C =60 degrees, EF=4.5cm, and DE=3.5cm. What is the perimeter of the trapezoid to the nearest mm?

Answer 1

Drop a perpendicular from G on CD to F.

Now you have a rectangle GDEF with sides 3.5 and 4.5

Also, triangle CGF where
CG = 3.5/√3
CF = 7.0/√3

Now the perimeter is easy - add up three sides of the rectangle, and the triangle.