physics question waves

hi, please could I have some help on this question? I'm confused how statement a is correct? I thought for interference to take place, waves must be emitted from coherent sources so the waves must have a zero or constant phase difference?
here is the question: https://ibb.co/0qt4KTJ
thanks!

Well, they don’t have to be in phase when they leave the speaker. Ie they could be 180 out of phase when they leave the speaker, that would merely shift where the zero amplitude point was.
Bit of a smart arse question rather than being a decent test of understanding waves and phase

oh, so for this type of interference, coherent sources aren't required?

hi, please could I have some help on this question? I'm confused how statement a is correct? I thought for interference to take place, waves must be emitted from coherent sources so the waves must have a zero or constant phase difference?
here is the question: https://ibb.co/0qt4KTJ
thanks!

oh, so for this type of interference, coherent sources aren't required?

What do you understand by "waves must have a zero or constant phase difference"?
Two important questions concerning what you are asking:
What are the conditions for two waves to interfere?
What are the conditions for an observable interference pattern to occur between the waves from two sources?

1) What do you understand by "waves must have a zero or constant phase difference"?

Two important questions concerning what you are asking:

2a) What are the conditions for two waves to interfere?

2b) What are the conditions for an observable interference pattern to occur between the waves from two sources?

In order for interference to take place, the waves must have the same frequency and zero or constant phase difference?

Which question are you answering? Q2a or Q2b? Or both Q2a and Q2b?

In order for interference to take place, the waves must have the same frequency and zero or constant phase difference?

It was for both sorry