Deducing capacitance from a wave form

[Phillolol]

I have been given the following task:

"Calculate the value of t/RC at which the waveform crosses zero, and hence use the oscilloscope measurement to deduce the value of the capacitance."

We are using the inverting input on op amps, so when the square wave is high it the wave slopes downwards.

I am unsure wether to use the charging or discharging formula, or how to deduce the capacitance from the result.

 

[Harald Kapp]

I am unsure wether to use the charging or discharging formula,

Both will give the same result.

how to deduce the capacitance from the result.

When you know the time constant tau = R × C and you know R, then you can calculate C.