Finding the root of a function y(x) refers to finding values of x for
which y(x)=0.
This is often used as a method of solving equations. For example, consider the
equation
x - 4 = 2.
One method of approaching this might be to reformat the equation so that one
side of the equation is equal to zero. Subtracting the 2 from both side in the above
example would give us
x - 6 = 0.
This particular example is fairly trivial, but suppose you have the equation
x2 + x = 6.
This could be reformatted as
x2 + x - 6 = 0
or
(x + 3) (x - 2) = 0
and the equation can be easily soved by inspection.