Equations and systems of equations

# biquadratic equations

A **biquadratic equatio**n is a 4-degree equation without the terms of degree 1 and 3.

To solve a biquadratic equation you have to do a change of variable: z = x^{2}. Then you have to solve the quadratic equation and finally undo the change.

Example 1:

Example 2:

z = -1 →Φ

**Exercise**. Solve the following equations:

a) x

^{4}- 25x^{2}+ 144 = 0b) x

^{4}+ 2x^{2}- 3 = 0c) x

^{6}+ 9x^{3}+ 8 = 0Solutions: a) ±3, ±4; b) ±1; c) -2, -1

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