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# Sketching Cubic Curves? watch

1. A question im trying to answer requires me to show that f(x)=0 has a root near to x=5 given that f(x)= x^3 - 5x^2 + 2.

Ofcourse, the first step would be to sketch the graph but how would you do this ( without finding the roots of f(x)=0 anyway)?
2. (Original post by sonic23)
A question im trying to answer requires me to show that f(x)=0 has a root near to x=5 given that f(x)= x^3 - 5x^2 + 2.

Ofcourse, the first step would be to sketch the graph but how would you do this ( without finding the roots of f(x)=0 anyway)?
You don't need to sketch it.

Find f(4) and f(5).

Look for a sign change.

As f(x) is continuous, it must cross the x axis as it changes from negative to positive.
3. Thanks that makes more sense
4. (Original post by sonic23)
Thanks that makes more sense
Good.

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