Let be p(x)=<span>(x^{2} -1 q(x)=</span><span>3(x+1) r(x)=1 the three coefficients of the equation a is a singular point of the equation if lim p(x) =0 x------>a so let's find a </span> lim p(x) = lim x²-1=a²-1=0 x------>a x------>a a²-1=0 implies a=+ or -1