If the coordinates of the vertices of a ∆ABC are A(- 1, 3, 2), B(2, 3, 5) and C(9, b, - 2), then ∠ A isequal to

Vertices of ∆ABC are A(-1 ,3,2), B(2, 3, 5) and c(3, 5, -2). AB=9+0+9=18CA=16+4+16=6and  BC=1+4+49=54∵ AB2+CA2=BC2∆ABC is right angled triangle at A. ∠A=90o