Răspuns :
a = 1 + 2 + 3 + .......+ 264 + 265 x 133
a = 264 x 265 / 2 + 265 x 133
a = 132 x 265 + 265 x 133
a = 265 x ( 132 + 133 )
a = 265 x 265
a = 265² → patrat perfect
a = 1 + 2 + 3 + ... + 264 + 265 × 133
a = ( 264 × 265 : 2 ) + ( 265 × 133 )
a = ( 132 × 265 ) + ( 265 × 133 )
a = 265 × ( 132 + 133 )
a = 265 × 265
a = 265²
→ a = pătrat perfect
a = ( 264 × 265 : 2 ) + ( 265 × 133 )
a = ( 132 × 265 ) + ( 265 × 133 )
a = 265 × ( 132 + 133 )
a = 265 × 265
a = 265²
→ a = pătrat perfect