Question: abcd is a parallelogram. if its diagonals are equal then find the value of angle abc?
Answer: Answer. In a parallelogram if two diagonals are equal, then the parallelogram is a rectangle.So, ABCD is a rectangle.It is known that each interior angle of a rectangle is 90 degree. Since ABC is an interior angle of rectangle ABCD, so measure of angle ABC is 90 degree.