The value of α in the pass band of constant k-low pass filter is?

• A. 2 cosh-1⁡(fc/f)
• B. cosh-1⁡⁡(fc/f)c) cosh-1⁡(f/fc)d) 2 cosh-1⁡(f/f
• C. cosh-1⁡(f/fc)
• D. 2 cosh-1⁡(f/fc)