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Without looking at the graph, use Newton’s Method to approximate the roots of if . What happened?

What happened?
Think about the shape of the graph of .
What is its range? What does that mean about the roots?

Newton's Method for Approximating Roots

Newton’s Method uses an iterative process to approximate a root (-intercept) of a function.

 Right side of upward parabola, vertex on negative y axis, 3 tick marks on x axis, all right of x intercept of parabola, labeled, from left to right, x sub 3, x sub 2, x sub 1, with vertical dashed segments, between the curve & x axis, 2 gray increasing lines, right line passes through x sub 2 & curve at x sub 1, left line passes through x sub 3 & curve at x sub 2.Begin with a point  near the root. Write the equation of its tangent line at .

The -intercept of this tangent line is .
Solve for  by setting .

 so .

 To calculate , solve for the root of the line tangent to  at . This process continues until the desired accuracy is met.

Therefore, each new approximation, , can be found using . Newton’s Method was very important before calculators were invented and represents an excellent example of an iterative process. For most functions it works well, but it is always possible to find examples where it does not.