I've been stuck on this problem, please help-

Select the correct answer from each drop-down menu. rewrite the formula to find voltage. the formula for electrical power (p, in watts) is where v is the voltage in volts and r is the resistance in ohms. for a particular brand of water heater, r is 32 ohms and p is 0.5 watts. the formula to find v is , and the voltage at which the heater operates is volts.

Evaluate cos2θ for cosθ = square root of 3/2

How do i simply this expression (quadratic formula basis) on a ti-84 or normal calculator?