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Open Middle Triangle Angle Sum Problem

Creation of this resource was inspired by this Open Middle problem by Franco D. Adkins:

Using the digits 1-9 at most one time each, fill in the blanks so that when you solve for , it is a whole number. You can use the app below to create such a triangle that's drawn to scale. Use the sliders to change the values of the digits (blanks) in each algebraic expression (for and ). How many solutions can you find? List them here:

You can create different variations of this problem by unlocking angle C and changing its measure.


For a version without the Show angle measures checkbox (lower left), click here.