If one angle of a cyclic quadrilateral is a right angle ,
then can we claim all the other three angles are also 
right angles?

Of course No.
Opposite angle to the given right angle must be 
right angle. The other two angles may not be
right angles. They should be supplementary ,thats all.
Plz drag A or C to see that B and D can vary

BENNY VARGHESE
PGT MATHS
JNV PATHANAMTHITTA

Radius = 3.9 (slider from 0.1 to 5, step 0.05)
O = (1.02, 1)
c = Circle(O, Radius)
D = Point(c)
f = Line(O, D)
C_1, B = Intersect(c, f)
A = Point(c)
C = Point(c)
g = Segment(D, A)
h = Segment(A, B)
i = Segment(B, C)
j = Segment(C, D)
α = Angle(D, C, B)
β = Angle(B, A, D)
γ = Angle(A, D, C)
δ = Angle(C, B, A)