Question

ABCD is a square. Determine angle DCA

Answer 1

In a square all four sides are equal, so are all the angles. So all the angles are 90°

Forming triangle DCA, the three sides are
AD, DC and CA

Since AD = DC, triangle DCA is an isosceles triangle.
So angle DCA = (180 - 90) / 2 = 45°

Answer 2

each angle is 90 degree diagonal ac bisects angle dcb . so dca is half of 90 degree that is 45 degree