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+21f(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+21f(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+21)=x+2+1-f(x)=-\left(|x+2|-1\right)=-|x+2|+1

    Writing x+21-|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+12=x+21-|x+2|+1-2=-|x+2|-1

  4. State the result and its features.

    f(x)=x+21,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+21=21=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+21=1  -|{-2}+2|-1=-1\;\checkmark. Since the maximum value is 1-1, the graph never reaches the xx-axis.

Answer

f(x)=x+21f(x)=-|x+2|-1

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