In a circuit L, C and R are connected in series with an alternating voltage source of frquency $f.$ The current leads the voltage by 45o. The value of C is
${1 \over {\pi f\left( {2\pi f\,L - R} \right)}}$
${1 \over {2\pi f\left( {2\pi f\,L - R} \right)}}$
${1 \over {\pi f\left( {2\pi f\,L + R} \right)}}$
${1 \over {2\pi f\left( {2\pi f\,L + R} \right)}}$
