How to Calculate the Missing Angle of a Rectangle

A calculator can assist in finding the fourth angle of a quadrilateral.
••• Jupiterimages/ Images

A rectangle is a geometric figure in which all four angles are 90 degrees. So if you have a missing side and it is a true rectangle, then you know the missing angle is 90 degrees. However, you could be working with a rectangle that is slanted. This is known as a parallelogram. To find the missing angle in such a case, you need to know that all the angles will add up to 360 degrees.

    Write out the three known sides. For example, assume you have angles of 120, 120 and 60.

    Write out an algebraic expression. Because you know the sum of all four sides must equal 360 degrees, your expression in the example will be 120 + 120 + 60 + X = 360.

    Solve for X. Add together all of the angles. Subtract the amount from 360. In the example, 60 degrees is the missing angle.

Related Articles

How to Find Angles in a Trapezoid
How to Find Angle Measures in a Quadrilateral
How To Calculate an Angle From Two Sides
How to Find a Missing Angle
How to Calculate a Tangent
How to Find Triangle Angle Measurements
Facts About Parallelograms
How to Calculate Triangle Dimensions
How to Figure Degrees in an Octagon
How to Find Angle Theta in Trigonometry
How to Find the Number of Sides of a Polygon
How to Find the Perimeter of a Rhombus When Given the...
How to Solve a Hexagon
How to Find Degrees in Polygons
How To: Degree to Radian Conversion
How to Find the Missing Side of a Right Triangle
How to Find an Angle of a Hexagon
How to Calculate the Volume of a Triangle
What Is a Two-Dimensional Shape?
How to Find the Volume of a Parallelogram

Dont Go!

We Have More Great Sciencing Articles!