51�Թ�

Thus the square root of 81 is 9, and the square root of 9 is 3, which is the biquadratic root of 81.

For n = 4, the biquadratic equation is solved with the help of the solution of the cubic.

Next to pure biquadratic equations, in respect of easiness of resolution, are such as want the second and fourth terms, and therefore have this form, x4 + qx� + s = 0.

The solution of cubic and of biquadratic equations, at first only in certain particular forms, but later in all forms, was mastered by Tartaglia and Cardan.

When a biquadratic equation contains all its terms, it has this form, x4 + Ax� + Bx� + Cx + D = 0, where A, B, C, D denote known quantities.