Question

The solution(s) of the equation $4x^5+4x^3=360x$ is

• A. $-10$
• B. $-i\sqrt{10}$
• C. $10i$
• D. $\sqrt{10}$

Answer 1

Answer: (B)

$-i\sqrt{10}$

The equation $4x^5+4x^3=360x$ be reduced to $4x(x^4+x^2-360)=0$
So, $x^4+x^2-360=0$
Assume $x^4=u^2$, $4x^2=u$
Then $u^2+u-360=0$
On factoring we get,
$(u-9)(u+10)=0$
So, $u=9,u=-10$
$x^2=9,x^2=-10$
$x=3,x=-i\sqrt{10}$
So, the option available is $-i\sqrt{10}$