what happens to the power of an electric circuit if the resistance is decreased?? explain?? i know that as the power increases the resistance decreases why is that??

Power = voltage^2 / resistance.

Think again about what you "know". Resistance does not decrease with increased power. For some things, like incandescent light bulbs, it goes up. Usually it stays the same.

P = I*V = V^2/R

Assume the circuit voltage (V) stays the same. What happens to power (P) when R decreases?