Bunuel
Circle P above circumscribes rectangle ABCD. What is the value of w°+x°+y°+z°?
(1) ABCD is a square.
(2) EF is a diameter of the circle P.
RamseyGoonerPlease look at the attached figure, where O is the center. O need not be on EF, and could be anywhere whereever the circle has its center.
Property:
The angle subtended on a particular arc ( for example, minor arc AE here) from the center of the circle will be TWICE of the angle subtended from anywhere on the circumference.
So, Angle AOE = 2*angle ABEThus \(\angle \)AOD = Angle AOE + angle EOD = 2*angle ABE+2* angle ECD=2w+2y=2(w+y)
Let us check the statements:-
1) ABCD is a square
So the diameter will meet at the center, and thus, lines AO and BO are diameter if extended further.
The diameter intersect at 90 to each other => angle AOD=90=2(w+y)...w+y=45
Similarly x+z=45, and w+x+y+z=45+45=90
Sufficient
2) EF is the diameter of the circle.
So center is on EF, but we cannot say anything about the angles subtended.
Insufficient
A
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