Question

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

Answer 1

a=3+6+9+....+75-75=3(1+2+3+....+25)-75=(3·25·26)/2-75=3·25·13-75=975-75=900=30·30=30² (adica patrat perfect)

Answer 2

a=3+6+9+...+75 -75 =3×(1+2+3+...+25)-75= 3×25×26÷2 -75=975-75=900= 30²