PSAT Math : Parallelograms

Study concepts, example questions & explanations for PSAT Math

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Example Questions

Example Question #172 : Plane Geometry

ABCD is a parallelogram. BD = 5. The angles of triangle ABD are all equal. What is the perimeter of the parallelogram?

Figure_1

Possible Answers:

\displaystyle 15

\displaystyle 20

\displaystyle 15\sqrt{3}

\displaystyle 10\sqrt{3}

\displaystyle 11\sqrt{2}

Correct answer:

\displaystyle 20

Explanation:

If all of the angles in triangle ABD are equal and line BD divides the parallelogram, then all angles in triangle BDC must be equal as well.

We now have two equilateral triangles, so all sides of the triangles will be equal.

All sides therefore equal 5.

5+5+5+5 = 20

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