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| Math Central | Quandaries & Queries |
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Question from Bruce, a student: The equation is x2-12. I need to find the x-y intercepts and horizontal intervals (increasing & decreasing) I would have thought the y intercept would be (0,-12) however the book came up with something different. |
Hi Bruce,
The y intercepts of y = x2 - 12 are the points where the graph crosses the y-axis. Since points on the y-axis are precisely the points that have their x-coordinates equal to zero you can find the y-intercepts by substituting x = 0 and solving for y. Thus
y = 02 - 12 = -12
Thus I agree with you, there is one y-intercept at (0, -12).
Likewise the x-intercepts are obtained by substituting y = 0. In this case
0 = x2 - 12 so x = ±√12
Penny
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