Co-ordinate geometry/algebra?

Question

ABCD is a rectangle in which the co-ordinates of A and C are (0,4) and (11,2) respectively. The gradient of ab is -5.
1)Find the equations of ab and bc
2)Show that the co-ordinates of b are (1,-1)
3)Find the area of rectangle ABCD

The points A(2,5) and B(-4,13) lie in the opposite ends of a diameter of a circle with centre C.
a) Find the radius and centre of the circle
b)Find the equation of the circle in the form x^2+y^2 +px+qy+c=0
c)Find the equation of the normal at a and the tangent of b

If you can do ANY of these please do, and put how you do it. Sorry-but i got stuck!!!

Answer 1

AB) y-4= -5x
CB) y-2=1/5(x-11)
Intercept
y=-5x+4 so
-5x+2= 1/5 (x-11)// -25x+10= x-11 so x= 21/26
If AC is a diagonal the slope of AB can be
1=( m+5)/(1-5m) so 1-5m= m+5 and m = -2/3 or

1= (-5-m)/(1-5m) so 1-5m= -5-m and m=3/2 but not -5
Check
2)Center (-1,9) radius ^2= 9+16 =25 so r=5
x^2+y^2+2x-18y+27=0

slope AB = -8/6= -4/3 which is the slope of the normal at A
y-5 = -4/3(x-2)

Tangent at B
y-13=3/4(x+4)