Diagonals of rectangle ABCD intersect at point O. Find the angle between the diagonals

The diagonals of the rectangle ABCD intersect at point O. Find the angle between the diagonals of the parallelogram angle DCO = 40 °

At the beginning of the problem, we are talking about a rectangle, so we will solve from the point of view that ABCD is a rectangle.

Let’s denote one of the angles between the diagonals of the rectangle as <COD, and consider the triangle COD. It is known by the condition <DCO = 40 °.
But given that the diagonals in the rectangle are equal, their halves are also equal, DO = CO, which means that the DCO triangle is isosceles.
This means that the angles of such a triangle at the base DC are equal. <CDO = <DCO = 40 °. Now you can find the angle between the diagonals: <COD = 180 – (<CDO + <DCO) = 180 – (40 ° + 40 °) = 100 °



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