i really need someone who can check whether i'm doing

it right or not.. =)

Question:

Design a first order Butterworth low pass filter with cut-off frequency fo = 20 kHz and the gain K = 1

fo = 20kHz

K = 1

When K = 1, we can ignore R1 and Rf

formula :

ωo = 1/RC

2∏fo = 1/RC

Set R = 1kΩ

2∏fo = 1 / (1000) C

C = 1 / (1000)(2∏fo)

C = 7.96nF

Answer: R = 1kΩ ; C = 7.96nF

My answer is correct?