piyush26 wrote:

Is x^2 > y^2?

(1) x^2 − x > y^2 − y

(2) x > y

\({x^2}\,\,\mathop > \limits^? \,\,{y^2}\)

\(\left( 1 \right)\,\,{x^2} - x > {y^2} - y\,\,\,\,\left\{ \matrix{

\,{\rm{Take}}\,\,\left( {x,y} \right) = \left( {2,0} \right)\,\,\,\, \Rightarrow \,\,\,\left\langle {{\rm{YES}}} \right\rangle \,\, \hfill \cr

\,{\rm{Take}}\,\,\left( {x,y} \right) = \left( { - 1,1} \right)\,\,\,\, \Rightarrow \,\,\,\left\langle {{\rm{NO}}} \right\rangle \,\, \hfill \cr} \right.\)

\(\left( 2 \right)\,\,x > y\,\,\,\,\left\{ \matrix{

\,{\rm{Take}}\,\,\left( {x,y} \right) = \left( {1,0} \right)\,\,\,\, \Rightarrow \,\,\,\left\langle {{\rm{YES}}} \right\rangle \,\, \hfill \cr

\,{\rm{Take}}\,\,\left( {x,y} \right) = \left( {0, - 1} \right)\,\,\,\, \Rightarrow \,\,\,\left\langle {{\rm{NO}}} \right\rangle \,\, \hfill \cr} \right.\)

\(\left( {1 + 2} \right)\,\,\,\,{x^2} - {y^2}\,\,\,\mathop > \limits^{\left( 1 \right)} \,\,\,x - y\,\,\,\mathop > \limits^{\left( 2 \right)} \,\,\,0\,\,\,\,\, \Rightarrow \,\,\,\,\,{x^2} > {y^2}\,\,\,\,\, \Rightarrow \,\,\,\,\,\left\langle {{\rm{YES}}} \right\rangle\)

This solution follows the notations and rationale taught in the GMATH method.

Regards,

Fabio.

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Fabio Skilnik :: GMATH method creator (Math for the GMAT)

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