Algebra · real student question

The parent function f(x) = |x| is reflected in the x-axis and then translated 6 units down. Write the equation of the new function.

Question

The parent function f(x)=xf(x)=|x| is reflected in the xx-axis and then translated 66 units down. Write the equation of the resulting function.

Step-by-step solution

  1. Begin with the parent V. f(x)=xf(x)=|x| has vertex (0,0)(0,0), opens upward, and has arms of slope 1-1 on the left and +1+1 on the right. Its range is [0,)[0,\infty).

  2. Reflect in the xx-axis. Reflecting across the xx-axis replaces each output yy by y-y:

    f(x)=x-f(x)=-|x|

    The V now opens downward, arms of slope +1+1 then 1-1, with range (,0](-\infty,0]. (A reflection across the yy-axis would instead replace xx by x-x and change nothing here, since x=x|-x|=|x| — worth noting because the problem says only "reflected".)

  3. Translate 6 units down. Subtract 66 from the output:

    x6-|x|-6

  4. Describe the resulting graph.

    f(x)=x6,vertex (0,6), range (,6]f(x)=-|x|-6,\qquad \text{vertex }(0,-6),\ \text{range }(-\infty,-6]

    The maximum value is 6-6, attained only at x=0x=0.

  5. Check points and note there are no roots. At x=0x=0: 06=6  -|0|-6=-6\;\checkmark (the vertex). At x=3x=3: 36=9-3-6=-9, and the parent point (3,3)(3,3) indeed reflects to (3,3)(3,-3) then drops to (3,9)  (3,-9)\;\checkmark. Because the largest output is 6<0-6<0, the equation x6=0-|x|-6=0 has no solution — this graph never meets the xx-axis.

Answer

f(x)=x6f(x)=-|x|-6

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