In Cartesian coordinates, the symmetric point of point a (5,0) about the origin is C 1. Please write the coordinates of point C directly 2. If point B is in the first quadrant, angle OAB = angle oba, and the symmetric point of point B about origin o is point D Judging the shape of quadrilateral ABCD (to be proved)

In Cartesian coordinates, the symmetric point of point a (5,0) about the origin is C 1. Please write the coordinates of point C directly 2. If point B is in the first quadrant, angle OAB = angle oba, and the symmetric point of point B about origin o is point D Judging the shape of quadrilateral ABCD (to be proved)

The first question should be very simple to know that the C point is (- 5,0)
Second question: because a (5,0), B is in the first quadrant, point D is B symmetrical about the origin, and point C is a symmetrical about the origin
So AC / / BD, angle OAB = angle OCD
So the four sides of ABCD are rectangle or isosceles trapezoid
And because angle OAB = angle oba
So the angle OAB is not equal to 90 degrees
So the quadrilateral ABCD is isosceles trapezoid
This proof should be OK