Question
Find roots of polynomial $$ p(x) = -10x^4-9x^2 $$
Answer
The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 0\\[1 em]x_2 &= \dfrac{ 3 \sqrt{ 10}}{ 10 }i\\[1 em]x_3 &= -3 \dfrac{\sqrt{ 10 }}{ 10 }i \end{aligned} $$Explanation
Step 1:
Factor out $ \color{blue}{ -x^2 }$ from $ -10x^4-9x^2 $ and solve two separate equations:
$$ \begin{aligned} -10x^4-9x^2 & = 0\\[1 em] \color{blue}{ -x^2 }\cdot ( 10x^2+9 ) & = 0 \\[1 em] \color{blue}{ -x^2 = 0} ~~ \text{or} ~~ 10x^2+9 & = 0 \end{aligned} $$One solution is $ \color{blue}{ x = 0 } $. Use second equation to find the remaining roots.
Step 2:
The solutions of $ 10x^2+9 = 0 $ are: $ x = \dfrac{ 3 \sqrt{ 10}}{ 10 } i ~ \text{and} ~ x = -3 \dfrac{\sqrt{ 10 }}{ 10 } i $.
You can use step-by-step quadratic equation solver to see a detailed explanation on how to solve this quadratic equation.
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