If y= 3x^2 + x^2 - 5 and z= x^2 - 12, which polynomial is equivalent to 2(y+z)? *Please show your work*​

If the angle bisectors of a pair of opposite angles of a quadrilateral are the opposite sides of a parallelogram formed by the two angle bisectors and two sides of the quadrilateral, is the quadrilateral always a parallelogram? explain your answer.