如下从Kline的古今数学思想中copy下来。
说四次方程的求解呢就是替换之后将左右变形，使得左边成为一个平方式，右边是一
个二次式，然后假设右边二次式的判别式为零，于是babalala。但这个假设为何可以随
便做出呢？
success in solving the quartic. The method is due to Lodovico Ferrari and
was published in Cardan's Ars Magna; we dcscribe it in modern notation and
with literal coefficients to show thc gcnerality. The equation is
(18)
x 4 + bx 3 + cx 2 + dx + e = O.
By transposition we get
( 19)
x 4 + bx 3 = -cx 2 - dx - e.
Now complete the square on the lcft sidc by adding ( bx r. This givcs
(X2 +
