A resistive voltage divider is totally unpractical at your current requirements. Even a linear regulator would produce (48-36)*15= 180W of heat. This would require a huge heatsink.
This is a job for a SMPS buck converter with an overall efficiency of ~85% which would reduce the power dissipation to about 30W.
i need a circuit to stepdown 48 Volts (Which are being generated through a rectifier) to 36 Volts, 6 Amp is constant power which will be utilized. voltage can be varried from 36 to 40 Volts.
Put two IN5404 diodes in parallel (18 cents each) and this will drop about 0.7v and allow 6A of current to flow without overheating the diodes. Do this 15 times and you have a 10v drop.
Alternatively get four 3R3 10watt resistors and put them in parallel. Do this again and put the first quad of resistors in series with the second quad of resistors.
Put either of these "droppers" on the positive line and it will drop about 10v.