The Setup: To find the range of a rational function, set it equal to , rearrange into a quadratic in , and force the discriminant to be non-negative - because is required to be real. The values of that survive are exactly the range.
Step 0: Confirm the function is defined everywhere. The denominator has discriminant , so it never hits zero and the expression is defined for all real . Without this, chunks of the range argument could be vacuous.
**Step 1: Create the quadratic in .**
Collecting terms:
**Step 2: Handle the case separately - the discriminant method assumes a genuine quadratic.** If the coefficient vanishes and this is not a quadratic at all; it degenerates to , giving . So is attained, at , and indeed . It sits inside the range we are about to derive, so the final answer is unaffected - but the case has to be dismissed explicitly, not ignored.
**Step 3: Enforce the discriminant for .** Real requires . Noticing that keeps this tidy:
Since , divide throughout by 4:
Step 4: Difference of squares. With and :
Dividing by 3 and negating the first bracket flips the inequality:
Step 5: Confirm both endpoints are actually reached. An inequality gives bounds; it does not by itself prove they are attained, and the stem's wording requires that the function really does climb to .
* : the quadratic becomes , i.e. , so . Check: .
* : it becomes , i.e. , so . Check: .
Both are hit exactly once, at the two points where the discriminant is zero. The maximum value is therefore .
Final Answer: 9