Question
Question: Let f(x) = x<sup>2</sup> + 4x + 1, then –...
Let f(x) = x2 + 4x + 1, then –
A
f(x) > 0 for all x
B
f(x) < 1 when x ³ 0
C
f(x) ³ 1 when x £ – 4
D
f(x) = f(–x) for all x
Answer
f(x) ³ 1 when x £ – 4
Explanation
Solution
Since f(x) is a quadratic expression having real roots,
\ f(x) does not have the same sign for all x
Now f(x) ³ 1 ̃ x2 + 4x + 1 ³ 1
̃ x2 + 4x ³ 0 ̃ x £ – 4 or x ³ 0