BIQUADRATIC, an adjective used in mathematics to refer to the fourth power of a quantity; that is, to the square of a square. It is used in connection with equations or algebraic func tions. The equation ax4-1-bx3+cx2-1-dx+e=o is a biquadratic equation, since the highest power of the unknown quantity (x) is the fourth; that is, x4 is the square of x2, or the square of the square of x (the bi, two ± quadratus, square). The general bi quadratic equation was first solved by Lodovico Ferrari (1522 c. 156o) and was published by Cardan in his Ars Magna (I545)• Excepting in the above cases and in connection with a few geo metric figures the word "quartic" is used instead of "biquadratic." (See EQUATIONS.)