Question

arata ca nr este patrat perfect a = 3+6+9+.......+75-75

Answer 1

a=3+6+9+....+75-75
a=3(1+2+...+25)-75
a=3×25×26:2-75
a=75x13-75
a=900
a=30² este patrat perfect 

Answer 2

a=3+6+9+....+75-75
a=3×(1+2+3+...+25)-75
a=3×25×(25+1):2-75
a=3×25×26:2-75
a=75×13-75
a=975-75
a=900 a=30 la puterea 2 => este patrat perfect