It is known that (k ^ 2-1) x ^ 2 + kx-3k + 1 = 0 is a linear equation with one variable. Find the value of K

It is known that (k ^ 2-1) x ^ 2 + kx-3k + 1 = 0 is a linear equation with one variable. Find the value of K

According to the theme
k^2-1=0 ==> k=±√2