in the event that you don't have a calculator, you can estimate this. think of the nearest perfect squares to 39 ... 36. the square root of 36 is 6. this perfect square is LESS than 39, so find the next one that's LARGER: 49. the square root of 49 is 7. because 39 is between 36 and 49, you know that the ROOT of 39 is between the roots of those perfect squares: √36 = 6, and √49 = 7. therefore, you know that √39 lies between 6 and 7 on a number line.