Answer :
by the properties of rectangle opposite sides are parallel, the diagonals are equal and bisect each other.
hence, if the diagonals of a parallelogram are equal then it will be a rectangle
hence, if the diagonals of a parallelogram are equal then it will be a rectangle
if diagonals are equal
bc ll ad
ab is the transeversal therefore angle dab and cba will be equal to 90'
therefore in a llgm one angle is 90' then its a rectangle