Yes, a 6+2-pin can be used in a video card's 8-pin socket/receptacle, as an 8-pin.
I saw the 8 pin cable in the PSU box and I thought different. thank you for answering I had to be sure
Well, PSUs come with 4+4-Pin and/or 8-pin to provide power to the CPU, as well as separate cable(s) to power your video cards which can come in a variety of 6-pin, 6+2-pin and/or 8-pin. However, there are physical differences between the CPU 8-pin and PCIE 8-pin. Also the male and female 8-pin sockets are "keyed" to prevent users from incorrectly plugging in the wrong 8-pin (unless you try really hard), and are usually labelled "CPU" and "PCIE" right on the male sockets, which you would plug into the female ones. Whether you use the 6+2-pin or the 8-pin PCIE socket to plug into the card 8-pin female socket is up to you.
Hope that clarifies it.