Solve x^4-11x^2+28=0

$$x ^ { 4 } - 11 x ^ { 2 } + 28 = 0$$

Solve for x

$$x=-\sqrt{7}\approx -2.645751311$$

$$x=\sqrt{7}\approx 2.645751311$$

$$x=2$$

$$x=-2$$

Steps Using the Quadratic Formula

Substitute t for x^{2}.

$$t^{2}-11t+28=0$$

All equations of the form ax^{2}+bx+c=0 can be solved using the quadratic formula: \frac{-b±\sqrt{b^{2}-4ac}}{2a}. Substitute 1 for a, -11 for b, and 28 for c in the quadratic formula.

$$t=\frac{-\left(-11\right)±\sqrt{\left(-11\right)^{2}-4\times 1\times 28}}{2}$$

Do the calculations.

$$t=\frac{11±3}{2}$$

Solve the equation t=\frac{11±3}{2} when ± is plus and when ± is minus.

$$t=7 t=4$$

Since x=t^{2}, the solutions are obtained by evaluating x=±\sqrt{t} for each t.

$$x=\sqrt{7} x=-\sqrt{7} x=2 x=-2$$