Rotate the triangle APB 90 counterclockwise around A to get the triangle AP 1D== "Triangle AP 1D is a right triangle, AP = AP1= = > PP 1=√2, angle APP 1 = 45.

PP 1=√2，PD=√7，p 1D = 3 = = & gt； P1d 2 = PD 2+p1p 2 = = > triangle PP 1D is a right triangle.

= => Angle p1pd = 90.

Angle APD= angle APP 1+ angle p 1pd = 45+90 = 135.