Show that the Geometric series Σ r^n-1=1+r+r^2+r^3+r^4+…..,where r > 0 , is convergent if r < 1and diverges if r ≥ 1| Geometric series solved problems

Show that the Geometric series Σ r^n-1=1+r+r^2+r^3+r^4+…..,where r > 0 , is convergent if r < 1and diverges if r ≥ 1| Geometric series solved problems