Question

Daca x ∈ N si 1+3+5+...+(2x-1)=100,atunci x este......

Answer 1

1+3+5+...+(2x-1)=
=(2*1-1)+(2*2-1)+...+(2x-1)
=2(1+2+3+...+x)-x
=2*x(x+1)/2-x
=x(x+1)-x
=x²
x²=100=10² => x=10