alimad wrote:

In the rectangular coordinate system, are the points (r,s) and (u,v) equidistance from the origin ?

1.r+s =1

2. u = 1-r and v=1-s

Please provide explaination

(1) Only gives us information about r and s, u and v could be anything. INSUFFICIENT, eliminate AD.

(2) Plug in.

(r,s)=(0,0), (-1,-1), (1,1), (1,0), (0,1).

(u,v)=(1,1), (2,2), (0,0), (0,1), (1,0).

Equidistant from (0,0)? No, no, no, yes, yes.

INSUFFICIENT, eliminate B.

Now go back to (2) and look at all the (r,s) that resulted in (u,v) being equidistant from the origin. All r+s=1 worked, so you know that (1)+(2) is SUFFICIENT, eliminate E.

Answer: C.

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