What is the resonant frequency of a parallel RLC circuit if R is 4.7 kilohms, L is 90 microhenrys and C is 100 picofarads?

The resonant frequency formula is f = 1 / (2π√(LC)). Just as in similar circuit math problems, the parallel resistance (4.7 kilohms) is a distractor and has no effect on the resonant frequency of the circuit. First, express the values in standard units: L = 90 × 10^-6 H and C = 100 × 10^-12 F. Multiply these to get 9,000 × 10^-18. Taking the square root gives roughly 9.487 × 10^-8. Multiply this result by 2π to get about 5.96 × 10^-7. Taking the reciprocal (1 divided by this number) yields exactly 1,677,721 Hz. When converted and rounded, you get the correct answer of 1.68 MHz.