The letter "x" is often used in algebra to mean a value that is not yet known. It is called a "variable" or sometimes an "unknown". In x + 2 = 7, x is a variable
Hello,
Assume Ax+By+Cz+D=0 the plane 's equation.
p=(0,0,0)==>A*0+B*0+C*0+D=0==>D=0
q=(0,1,0)==>A*0+B*1+C*0+0=0==>B=0
r=(1,2,3)==>A*1+0*2+C*3+0=0==>A=-3C
Let C=1==>A=-3
An equation of the plane is -3x+z=0
