1. Find the derivative of the function $f(x)$ using the quotient rule.
f′(x)=dxd(x−2kx2−5x+3)
Using the quotient rule:
f′(x)=(x−2)2(2kx−5)(x−2)−(kx2−5x+3)(1)
f′(x)=(x−2)22kx2−4kx−5x+10−kx2+5x−3
f′(x)=(x−2)2kx2−4kx+7
2. State the condition for the function to be increasing.
For f(x) to be an increasing function for all x=2, we require f′(x)≥0 for all x=2.
(x−2)2kx2−4kx+7≥0
Since (x−2)2>0 for all x=2, this inequality holds if and only if the numerator is non-negative:
kx2−4kx+7≥0for all x=2.
3. Formulate conditions for the numerator to be consistently non-negative.
If k=0, the numerator becomes 0x2−4(0)x+7=7≥0, which is valid for all real x.
If k=0, the quadratic expression must have a positive leading coefficient (k>0) and a non-positive discriminant (Δ≤0) so that it is always non-negative:
Δ=(−4k)2−4(k)(7)≤0
16k2−28k≤0
4k(4k−7)≤0
4. Solve the inequality to find the final range of $k$.
Solving 4k(4k−7)≤0 yields:
0≤k≤47
Combining this with the valid case k=0, the complete range of values for k is:
0≤k≤47
答案0≤k≤47