Algebra · real student question

Graph f(x) = |x| and g(x) = |x| - 9 in the same coordinate system and describe how the graph of g is related to the graph of f.

Question

Graph f(x)=xf(x)=|x| and g(x)=x9g(x)=|x|-9 in the same rectangular coordinate system, and describe how the graph of gg is related to the graph of ff.

Step-by-step solution

  1. Describe the parent graph. f(x)=xf(x)=|x| is the V-shaped absolute-value parent function: vertex at (0,0)(0,0), slope 1-1 to the left of the vertex and +1+1 to the right. Useful anchor points are (2,2)(-2,2), (1,1)(-1,1), (0,0)(0,0), (1,1)(1,1), (2,2)(2,2).

  2. Read the transformation from the algebra. In g(x)=x9g(x)=|x|-9 the 9-9 is applied outside the absolute value, so it changes the output rather than the input. Changes to the output move the graph vertically.

  3. Apply the shift to each anchor point. Subtracting 99 from every yy-value sends (0,0)(0,9)(0,0)\to(0,-9), (1,1)(1,8)(1,1)\to(1,-8), (1,1)(1,8)(-1,1)\to(-1,-8), (2,2)(2,7)(2,2)\to(2,-7) and (2,2)(2,7)(-2,2)\to(-2,-7).

  4. Note what does not change. No horizontal shift, no reflection, no stretch: the two branches keep slopes ±1\pm 1 and the opening still points upward. Only the vertical position moves.

  5. State the relationship. The graph of gg is the graph of ff translated 99 units downward, with the vertex relocated from (0,0)(0,0) to (0,9)(0,-9).

Answer

g(x)=f(x)9: the graph of f shifted down 9 units, vertex (0,9)g(x)=f(x)-9:\ \text{the graph of }f\text{ shifted down }9\text{ units, vertex }(0,-9)

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