How to execute a command when a player is at a specific coordinate? (1.14+)

How do i execute a command whenever a player is at a specific coordinate in 1.14+ Minecraft commands?

Im trying to execute a tellraw when they are at a specific coordinate

I tried doing this in a repeating/always active/unconditional command block

execute if entity @p positioned x y z

then i would put a comparator for power to the impulse/need redstone/unconditional command block with the command

tellraw @p "Example"

but nothing would happen.

I tried putting the tellraw with the execute command block but it would just repeat the tellraw, or making the command block not on repeat does nothing.

execute if entity @p[x=87,y=77,z=20,dx=0,dy=0,dz=0] run tellraw @p "Example"