Algebra · real student question

Graph f(x) = -|x + 5| - 4. Identify the vertex, the direction it opens, the intercepts, and the range.

Question

Graph f(x)=x+54f(x)=-|x+5|-4. Identify the vertex, which way the graph opens, its intercepts, and its range.

Step-by-step solution

  1. Match the equation to vertex form. Comparing with f(x)=axh+kf(x)=a\left|x-h\right|+k:

    a=1,h=5  (since x+5=x(5)),k=4a=-1,\qquad h=-5\ \ (\text{since }x+5=x-(-5)),\qquad k=-4

    so the vertex is (5,4)(-5,-4). Rewriting x+5x+5 as x(5)x-(-5) before reading hh prevents the usual sign mistake.

  2. Determine the direction and steepness from aa. Because a=1<0a=-1<0 the graph opens downward — an upside-down V — and because a=1|a|=1 the arms have slopes +1+1 (left of the vertex) and 1-1 (right of it), the same steepness as the parent x|x|.

  3. Build the graph as a sequence of transformations. Starting from y=xy=|x|: shift left 55 (because x+5x+5 is zero at x=5x=-5), reflect across the xx-axis, then shift down 44:

    x    x+5    x+5    x+54|x|\;\to\;|x+5|\;\to\;-|x+5|\;\to\;-|x+5|-4

  4. Plot a few points either side of the vertex. Using the slope ±1\pm 1 from (5,4)(-5,-4):

    f(7)=24=6,f(6)=14=5,f(5)=4,f(4)=5,f(3)=6f(-7)=-2-4=-6,\quad f(-6)=-1-4=-5,\quad f(-5)=-4,\quad f(-4)=-5,\quad f(-3)=-6

    The symmetry about the vertical line x=5x=-5 is visible in these values, which is a good check that the horizontal shift was applied correctly.

  5. Read off the intercepts and range. The yy-intercept is f(0)=54=9f(0)=-|5|-4=-9, giving the point (0,9)(0,-9). For xx-intercepts you would need x+54=0-|x+5|-4=0, i.e. x+5=4|x+5|=-4, which is impossible since an absolute value is never negative — so there are none. The maximum output is 4-4 at the vertex, so the range is

    (,4](-\infty,-4]

Answer

Vertex (5,4); opens downward; y-intercept (0,9); no x-intercepts; range (,4]\text{Vertex }(-5,-4);\ \text{opens downward};\ y\text{-intercept }(0,-9);\ \text{no }x\text{-intercepts};\ \text{range }(-\infty,-4]

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