I have trouble about pinging pc1 to pc3 and pc2 to pc3 but the pc3 can successfully ping pc1 and pc3.
This is EIGRP packet tracer that allows routers to connect pcs to pcs:

I have trouble about pinging pc1 to pc3 and pc2 to pc3 but the pc3 can successfully ping pc1 and pc3.
This is EIGRP packet tracer that allows routers to connect pcs to pcs:

Ok, I don't know how your configuration is, but what you can do is to follow the ICMP packets via the Simulation Feature in Packet Tracer. You will then be able to see on which router the packet stops, it'll show a blinking "X" on the packet – which symbolizes that the packet is dropped. If you then click on this packet (with the blinking "X") you can see a description of why it is stopped/dropped. Hopefully then you can figure out what causes the pings to not be successful.
Here's a quick tutorial on how to use the Simulation Mode in Packet Tracer: