Answer:
Geometric proof in the explanation.
Step-by-step explanation:
Draw a square. A square has all equal sides and it's 4 angles each measure 90 degrees.
Draw a diagonal which will cut the square into two congruent isosceles right triangles.
So this will give you a 45-45-90 triangle.
I drew the triangle in the picture.
Tangent is opposite over adjacent so we don't need to find the hypotenuse in terms of a ( a is positive).
So tan(45)=a/a=1.
