Question

The number of real roots of the equation $x^5+3x^3+4x+30=0$ is

• A. 1
• B. 2
• C. 3
• D. 5

Answer 1

Answer: (A)

Let $f(x)=x^5+3x^3+4x+30$
$\Rightarrow f^{{}^{\prime }}(x)=5x^4+9x^2+4$
$\Rightarrow f^{{}^{\prime }}(x)>0$ for all $x\in R$
Hence, the $f(x)=0$ has only one real root.