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Electrical Engineering tutorial question help

Hi, as the title suggests I've just got a little question regarding a tutorial question.
The question is as follows:

Components of a high-pass filter are 1 kΩ and 0.02 µF. Input voltage is 20∠0° V.Determine the cutoff frequency in Hz and magnitude of output voltage when inputvoltage frequency is 2 kHz, 15 kHz, 40 kHz, and 100 kHz.

Now from my tutorial solutions, the solution is:

Cut-off frequencyω = 1/RC f = 1 / (2π RC) = 7.96 kHz
Magnitude of output voltage is VOUT = ωRC/ √[(1 + (ωRC)2] x Vin
at 2 kHz: VOUT = 4.87 V
at 15 kHz: VOUT = 17.67 V
at 40 kHz: VOUT = 19.62 V
at 100 kHz VOUT = 19.94 V

Now my question is, how do you determine the Vin in order to use the given formula.

Thanks.