consistent(dependent)---> coinsiding lines

If the equations on a give equation have they only have one 

solution

a1/a2 is  equal to b1/b2 is  equal to c1/c2<<< construction of the 

coefficient of the variables in the equations

there are infinite solutions... but you need to put parameters

The graphical solution is any point on the two identical straight lines.

to find the solution of the given system you need to find the value interms of x and y
and replace them with other variable.. like  the solution of given system  : (1-b,b) which y=t... it is most ad visable to change the variable of the rightmost in the equation...