"Did you say hello?"
Translation:Ddwedaist ti helo?
That's just the way of forming a question in the past tense.
Dwedaist ti helo "You said hello"
Ddwedaist ti helo "Did you say hello?"
Bwytaist ti swper "You ate supper"
Fwytaist ti swper "Did you eat supper?"
Parciaist ti'r car "You parked the car"
Barciaist ti'r car? "Did you park the car?"
Golchaist ti'r car "You washed the car"
Olchaist ti'r car? "Did you wash the car?"