The given linear equation is 2x+cy=8.
Now, by condition, x and y-coordinate of given linear equation are same, i.e., x=y.
Put y=x in Eq. (i), we get
2x+cx=8
`implies " " cx=8-2x`
`implies " " c=(8-2x)/(x),x ne 0`
Hence, the required value of c is `(8-2x)/(x)`.