First, k can be equal to 0. When k is not equal to 0, both sides of the equation are divided by16k 2 at the same time, and the result is 7k 2+2-4k 4 = 0.

Let k2 = t(t >；; 0) get 4t 2-7t-2 = 0 and get t=2 or t=- 1/4 (rounded), so k can be the plus or minus sign of two or zero.