thearch wrote:

I don't know whether it is forbidden to post questions from other sites. However, this is from

http://www.manhattangmat.com . I apologize in advance if I violate any rule.

Here comes the question:

C.

From 1 ) c + d = (r ^ 2)/(a + b)

= (a+b)^2 * (c-d)^2 / ( a+ b)

= (a+b)*(c-d)^2

(a + b) can or cannot be a perfect square ,hence insufficient.

From 2) (a + b) is a perfect square. ( still no clue about c + d )

Using 1 and 2. c + d = (a+b) (c -d ) ^2

= (x^2*y^3*z)^2 * (c - d ) ^2

= ((x^2*y^3*z) * (c - d )) ^2.( a perfect square)

Hence sufficient.

HMTG.