1. Rewrite as x3 + 8x2 -20 = f(x) where we want the x that makes f(x) = 0.
Plot a graph:
1. Guess x = -1, f(-1) = -13
2. Guess x = -2 f(-2) = 4
3. Use f(-2)/(-2-x) = -f(-1)/(x- -1) to get the next value of x, namely x = -1.77 to 2 decimal places
When x = -1.77 f(-1.77) = -0.482 Not yet close enough to zero. Because it is negative repeat step 3, but replace -1 and f(-1) with -1.77 and f(-1.77) respectively
4. Use f(-2)/(-2-x) = -f(-1.77)/(x- -1.77) to get x = -1.80 to 2 decimal places
When x = -1.80 f(-1.80) = -0.09
Repeat with
5. f(-2)/(-2-x) = -f(-1.80)/(x- -1.80) to get x = 1.80 to 2 decimal places
So one solution is x = 1.80 to 2 decimal places.
Try using the graph above to get two reasonable approximations to the other solution and repeat the above process.
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