Given rectangle pqrs with pq=qr, pq=sp, and sq=5√2. find rq. a) not enough info. b) √2. c) 5. d) 5√2

PQRS is a square. By definition of a square, it has 4 equal sides, in this case segments PQ, QR, RS and PS. Based on the given, all segments are equal as proof that PQRS is a square. Furthermore, this square has a units per segment. Thus, all 4 segments measure a units. 
SQ is the adjacent side, which cuts the square in triangles. 
a^2+a^2=(5√2)^2 hence, a=5 units. C is the correct answer.

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