Solve.
-$x ^ { 4 } - 30 x ^ { 2 } = 216$
A) $- 6,6 , - i \sqrt { 6 } , i \sqrt { 6 }$
B) $- \sqrt { 6 } , \sqrt { 6 } , - 6 i , 6 i$,
C) $6 , \mathrm { i } \sqrt { 6 }$
D) $- 36,6$

Question

Quizplus · Accepted Answer

This equation can be solved by substituting $y = x^2$, turning it into a quadratic equation $y^2 - 30y - 216 = 0$. Solving this gives $y = 36$ and $y = -6$. Substituting back $x^2 = 36$ gives $x = 6$ and $x = -6$, and $x^2 = -6$ gives $x = i\sqrt{6}$ and $x = -i\sqrt{6}$.

Solve - x4−30x2=216x ^ { 4 } - 30 x ^ { 2 } = 216x4−30x2=216

Solve
- $x ^ { 4 } - 30 x ^ { 2 } = 216$