It tells us that an equation has how many solutions? It is very important to know about the number of solutions that an equation has—one, two, or more.

It depends on the nature of the system of equations, whether the equations are linear, quadratic, or other, so an equation tells the number of solutions based on its nature.

(x−1)(x+1)=x+1
x2−1=x+1
x2−1−x−1=0
x2−x−2=0
x2+x−2x−2=0
x(x+1)−2(x+1)=0
(x−2)(x+1)=0
x=2 ,x=−1
So the equation (x−1)(x+1)=x+1 has two real solutions.