Please help: Cubic fcn thru points (2,0), (1,3), tangent to x-axis at origin

vanessasmith

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hi everyone please help me with this problem I don't understand

Find the equation of the cubic function whose graph passes through the points (2,0) and (1,3) and is tangent to the x-axis at the origin. :-(
 
hi everyone please help me with this problem I don't understand

Find the equation of the cubic function whose graph passes through the points (2,0) and (1,3) and is tangent to the x-axis at the origin. :-(

Hint: General cubic equation: y(x) = A*x^3 + B*x^2 + C*x + D

What are your thoughts?

Please share your work with us ...even if you know it is wrong.

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Well since it passes through (2,0) I know that a factor of the equation will be x=-2. Since its tangent to the x-axis I think another zero is at the origin? I'm not too sure
 
Well since it passes through (2,0) I know that a factor of the equation will be x=-2. Since its tangent to the x-axis I think another zero is at the origin? I'm not too sure
Since x-axis is tangent to the curve at the origin, then x=0 must be a "repeated" root of the function. What does that tell you about the function?
 
I think you're almost there. Just a bit of putting the various pieces together. You've correctly identified that because the graph passes through the point (2, 0) there will be a root (or "zero") at x=2. Now you think the information that the cubic function is tangent to the x-axis at the origin tells you there's another root at x = 0. Well, perhaps looking up what it means for a graph to be tangent to the x-axis will help you. "If a graph is tangent to the x-axis, the graph touches but does not cross the x-axis at some point on the graph." Based on that, was your initial assessment correct? We also know that if the graph is tangent to the x-axis at some point (in this case the origin, x = 0) the slope is 0 at that point. What does that tell you? (Hint: You posted this in the "calculus" sub-forum; what concept have you learned that models the slope of a function?)

Finally, what information have you gained from the fact that the graph passes through the point (1, 3)? Here, you'll want to consider Subhotosh Khan's hint. What happens to the generic cubic equation Ax3 + Bx2 + Cx + D, when x = 1? What does it mean that the y-coordinate of that point is 3?
 
hi everyone please help me with this problem I don't understand

Find the equation of the cubic function whose graph passes through the points (2,0) and (1,3) and is tangent to the x-axis at the origin. :-(


the cubic function whose graph passes through the points (2,0)

and

the cubic function whose graph is tangent to the x-axis at the origin.

Tells us that the function is of the form:

y = A * x2 * (x - 2)

Now how do you propose to calculate the value of A?
 
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