Solve the equation.
-$x^{4}+8 x^{2}-9=0$
A) $\{\mathrm{i},-\mathrm{i}, 3 \mathrm{i},-3 \mathrm{i}\}$
B) $\{3,-3, i,-i\}$
C) $\{1,-1,3 \mathrm{i},-3 \mathrm{i}\}$
D) $\{1,-1,3,-3\}$

Question

Quizplus · Accepted Answer

This equation can be solved by substituting $y = x^2$, turning it into a quadratic equation $y^2 + 8y - 9 = 0$. Solving this gives $y = 1$ and $y = -9$. Substituting back $x^2 = y$, for $y = 1$ we get $x = \pm1$, and for $y = -9$ we get $x = \pm3i$.

Solve the Equation x4+8x2−9=0x^{4}+8 x^{2}-9=0x4+8x2−9=0 A) {i,−i,3i,−3i}\{\mathrm{i},-\mathrm{i}, 3 \mathrm{i},-3 \mathrm{i}\}{i,−i,3i,−3i} B) {3,−3,i,−i}\{3,-3, i,-i\}{3,−3,i,−i}

Solve the Equation $x^{4}+8 x^{2}-9=0$ A) $\{\mathrm{i},-\mathrm{i}, 3 \mathrm{i},-3 \mathrm{i}\}$ B) $\{3,-3, i,-i\}$