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Algebra · real student question

The function f(x) = |x + 2| - 1 is reflected in the x-axis and then translated 2 units down. Write the equation of the new function.

Question

The function f(x)=∣x+2∣−1f(x)=|x+2|-1 is reflected in the xx-axis and then translated 22 units down. Write the equation of the resulting function.

Step-by-step solution

  1. Identify the starting graph. f(x)=∣x+2∣−1f(x)=|x+2|-1 is a V opening upward with vertex at (−2,−1)(-2,-1), since ∣x+2∣=∣x−(−2)∣|x+2|=|x-(-2)| puts h=−2h=-2 and the trailing −1-1 puts k=−1k=-1.

  2. Reflect in the xx-axis by negating the whole output. This is the step that trips people: the minus sign must apply to the entire function, constant included, not just the absolute-value term:

    −f(x)=−(∣x+2∣−1)=−∣x+2∣+1-f(x)=-\left(|x+2|-1\right)=-|x+2|+1

    Writing −∣x+2∣−1-|x+2|-1 at this stage would be the classic error — the −1-1 becomes +1+1 under reflection, because the point (−2,−1)(-2,-1) flips to (−2,1)(-2,1).

  3. Translate 2 units down by subtracting 2.

    −∣x+2∣+1−2=−∣x+2∣−1-|x+2|+1-2=-|x+2|-1

  4. State the result and its features.

    f(x)=−∣x+2∣−1,vertex (−2,−1), opens downwardf(x)=-|x+2|-1,\qquad \text{vertex }(-2,-1),\ \text{opens downward}

    The vertex has returned to its original coordinates by coincidence — the reflection lifted it from −1-1 to +1+1 and the shift dropped it back by 22 — but the graph is genuinely different, now an upside-down V.

  5. Check with points. Original (0,f(0))=(0,1)(0,f(0))=(0,1); reflecting gives (0,−1)(0,-1) and shifting down 22 gives (0,−3)(0,-3). The final formula: −∣0+2∣−1=−2−1=−3  ✓-|0+2|-1=-2-1=-3\;\checkmark. Original vertex (−2,−1)→(−2,1)→(−2,−1)(-2,-1)\to(-2,1)\to(-2,-1), and the formula gives −∣−2+2∣−1=−1  ✓-|{-2}+2|-1=-1\;\checkmark. Since the maximum value is −1-1, the graph never reaches the xx-axis.

Answer

f(x)=−∣x+2∣−1f(x)=-|x+2|-1

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