# LC circuit, resonant frequency

I am working on the question in the image attached, and I am having trouble with part b)

I found part a by using the formula of resonant frequency for a first order LC filter: w=1/sqrt(LC), and by rearranging for L, and plugging in w=108 x 10^6 x 2pi, and C=25 x 10^-12.

For part b, I have rearrange the same equation for C, and have used the inductance found in a), and plugged in w=88 x 10^6 x 2pi, however this is wrong.

Any ideas is greatly appreciated. Thank you very much.

• Think about the capacitor in parallel.. Now you have to consider two caps. Not just one.. Sum of two capacitances will contribute for 88 MHz.. Do not ignore C already present with value of 25 pF – User323693 Jun 11 '18 at 3:09

For the second equation I used; $$C = \frac{1}{L\cdot(F^2)\cdot(pi^2)\cdot 4}$$ = 37.649 pF.