In rectangle ABCD O is the intersection point of the diagonals. Angle AOD = 140 find the angle ACD.

The diagonals of the rectangle intersecting at point O divide the rectangle into four isosceles triangles. Two identical in pairs. The sum of the angles of the triangles around the point O is 360 °. The angles AOD and BOC are equal to each other and equal to 140 °.
To find the sum of the other two angles, subtract the sum of the angles AOD and BOC from 360 °.
360 ° – (140 ° + 140 °) = 80 °.
The angles AOB and are equal to half 80 °.
СОD = 80 ° ÷ 2 = 40 °.
In an isosceles triangle COD, the angle at the apex of the triangle is 40 °, we find the angle OCD.
OCD = (180 ° – 40 °) ÷ 2 = 70 °.
Angle ACD = OCD = 70 °.
Answer: the angle ACD is 70 °.