But questions remainedâ€”the big three **unknowns** of who, why, and when.

Sometimes his x has to do duty twice, for different **unknowns**, in one problem.

He first divides by the factor x -x', reducing it to the degree m - I in both x and x' where m>n; he then forms m equations by equating to zero the coefficients of the various powers of x'; these equations involve the m powers xo, x, - of x, and regarding these as the **unknowns** of a system of linear equations the resultant is reached in the form of a determinant of order m.

The second class of cases comprises equations involving two **unknowns**; here we have to deal with two graphs, and the solution of the equation is the determination of their common ordinates.

Simultaneous equations in two **unknowns** x and y may be treated in the same way, except that each equation gives a functional relation between x and y.

Similarly if we have F more **unknowns** than we have equations to determine them, we must fix arbitrarily F coordinates before we fix the state of the whole system.

The number F is called the number of degrees of freedom of the system, and is measured by the excess of the number of **unknowns** over the number of variables.