How can l connect subwoofer and passive speaker on yamaha P3500s power amp (diagram please)

Solution
Depends on the subwoofer which you don't specify make model or available connections.
If the sub is active you could split the output of whatever is feeding the amp to it and the subwoofer. A high pass filter would be good to remove bass from the main speakers allowing them to play louder and cleaner.
If the sub is passive you could connect it to any unused speaker terminals since that amp has three different kinds. How well it would match levels with the main speakers is a matter of trying it. Might not work.
Depends on the subwoofer which you don't specify make model or available connections.
If the sub is active you could split the output of whatever is feeding the amp to it and the subwoofer. A high pass filter would be good to remove bass from the main speakers allowing them to play louder and cleaner.
If the sub is passive you could connect it to any unused speaker terminals since that amp has three different kinds. How well it would match levels with the main speakers is a matter of trying it. Might not work.
 
Solution