Bunuel
For how many values of \(x < 0\) does the equation \(0.1x^4 – 0.5x^2 – 1.4 = 0\) hold?
A. 0
B. 1
C. 2
D. 3
E. 4
Gentle note to all experts and tutors: Please refrain from replying to this question until the Official Answer (OA) is revealed. Let students attempt to solve it first. You are all welcome to contribute posts after the OA is posted. Thank you all for your cooperation!Let’s multiply the entire equation by 10.
We get, \( 1x^4 – 5x^2 – 14 = 0\)
Let’s us take x^2 = ‘a’ , so the equation becomes \( 1a^2– 5a– 14 = 0\)
\( 1a^2– 5a– 14 = 0\)
\( 1a^2– 7a +2a – 14 = 0\)
\( a(a– 7)+2(a – 7)= 0\)
\( (a-7)*(a+2) = 0\)
hence the values of a = 7, and a = -2
x^2 = 7 , hence X = + sqrt (7) and X = - sqrt (7).
x^2 = -2 , which is not possible. Square of a number remains positive.
for x <0, only ONE value satisfies the equation. X = - sqrt (7).
Thus,
Option B