Finding the intersection angle of two walls inside the home is useful for remodeling or planning the decor. Knowing the angle of a wall or floor intersection allows for accurate installation of special cabinets or shelving. Generally, determining the intersection angle of two plane surfaces, such as two walls, is taught in trigonometry classes in high school or during your postsecondary education. Using standard household items, you can carry out this process with a relatively high degree of accuracy.
Things You'll Need
 Tape measure or measuring stick
 Scientific calculator

Pick any points on each of the two walls, equidistant from each other, the floor and the corner, and measure the distance between them. The objective of this step is to create a triangular space enclosed by the measuring device and the walls. The accuracy of the final calculation increases with larger measurement sizes. This measurement is known as the "opposite" side of the triangle.

Measure the length between one of the chosen points on the wall and the corner. This distance is the same for both walls. The side of the triangle on the right, when facing the corner, is known as the "hypotenuse."

Divide half the length of the measurement between the two walls, the opposite side, by the length of the wall between the intersection and either measuring point, the length of the hypotenuse. This calculation determines the Sine of the angle.

Press the "Arcsin" button on your scientific calculator. This button will usually display "Arcsin" or "Inverse Sin."

Enter the previously established value for the Sine of the angle and press the "Enter" or "Answer" button. The arcsine function performs an inverse operation relating the angle that generates the Sine value, as determined by the measurements, for the input value. This response is given in degrees.

Multiply this Value by 2. The resulting product is the angle of the intersecting walls.
Tips & Warnings
 Ensure that your scientific calculator is in degree mode, otherwise it may yield a wrong number.
References
 "Trigonometry," Ninth Edition; Margaret L. Lial, John Hornsby, David I. Schneider, Callie J. Daniels; 2009
 Math on Web: The Arcsin Function
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