If the function $f(x) = 2x^2 - kx +7$, is increasing on [1, 2], then $k$ lies in the interval
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → $(-∞, 4)$
$f(x)=2x^2 - kx + 7$
For $f(x)$ to be increasing on $[1,2]$, the derivative must satisfy:
$f'(x) \ge 0$ on $[1,2]$
Compute derivative:
$f'(x)=4x - k$
Minimum value of $4x - k$ on $[1,2]$ occurs at $x=1$:
$4(1) - k \ge 0$
$4 - k \ge 0$
$k \le 4$
Therefore:
$k \le 4$