Question

If we know outer angle of triangle the inner angle be

Answer 1

An exterior angle of a triangle is equal to the sum of the opposite interior angles.

For more on this see Triangle external angle theorem.

If the equivalent angle is taken at each vertex, the exterior angles always add to 360° In fact, this is true for any convex polygon, not just triangles. See Exterior angles of a polygon. In the figure above, drag the triangle's vertices and see that this is

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