Alphabet Angles

Angle C is equivalent to 45º as its initial and terminal sides are the side and diagonal of a square, respectively.

We can construct additional squares indicated by the dotted lines. $\angle C \cong \angle A + \angle D$ , since both angles are created by the initial and terminal sides of a square. In addition, $\angle B \cong \angle D$ as they are both corresponding angles of two similar right triangles (created by dividing a 1X2 rectangle in half along its diagonal). This means that $\angle A + \angle D \cong \angle C \Rightarrow$ $\angle A + \angle B \cong \angle C$ . Therefore (since $\angle C \cong 45 ^{\circ}$ ), $\angle A + \angle B + \angle C \cong 45^{\circ} + 45^{\circ} = \boxed{90^{\circ}}$