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# C3 Numerical Methods Question watch

1. From Page 30 of the C3 Revision Guide

The equation x^3-4x^2-17x+50=0 has 3 real roots. Find intervals in the form (N, N+1) where N is an integer, in which each root lies.

2. Let f(x) = x^3 - 4x^2 - 17x + 50. Then

-x | f(x)
-4 | -10
-3 | 38
-2 | 60
-1 | 62
-0 | 50
-1 | 30
-2 | 8
-3 | -10
-4 | -18
-5 | -10
-6 | 20

f changes sign in the intervals (-4, -3), (2, 3) and (5, 6).
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3. Do they let you use iteration in these Qs?
How do you know what domain to use?
Do we just assume they'd give us say -10<x<10 or something?
4. (Original post by Jonny W)
Let f(x) = x^3 - 4x^2 - 17x + 50. Then

-x | f(x)
-4 | -10
-3 | 38
-2 | 60
-1 | 62
-0 | 50
-1 | 30
-2 | 8
-3 | -10
-4 | -18
-5 | -10
-6 | 20

f changes sign in the intervals (-4, -3), (2, 3) and (5, 6).
how did u knw 2 put those values in?
5. (Original post by mackin boi)
how did u knw 2 put those values in?
I started at x = 0 and worked outwards in both directions until I had found three sign-changes.
6. (Original post by Jonny W)
I started at x = 0 and worked outwards in both directions until I had found three sign-changes.
wat happens if it was inbetween 100 and 101???
7. (Original post by mackin boi)
wat happens if it was inbetween 100 and 101???
You'd have used common sense as you see if the values of the function you get from a certain value of x are nowhere near 0 you obviously need to change dramatically. You could also use a graph.
8. grafs are betta arent they?

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