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Show that there is a root for the equation x3 − 3x = 0 between 1 and 2.

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प्रश्न

Show that there is a root for the equation x3 − 3x = 0 between 1 and 2.

योग
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उत्तर

Let f(x) = x3 − 3x  

f(x) is a polynomial function and hence it is continuous for all x ∈ R

A root of f(x) exists if f(x) = 0 for at least one value of x

f(1) = (1)3 – 3(1)

= – 2 < 0

f(2) = (2)3 – 3(2)

= 2 > 0

∴ f(1) < 0 and f(2) > 0

∴ By intermediate value theorem, there has to be point ‘c’ between 1 and 2

Such that f(c) = 0

∴ There is a root of the given equation between 1 and 2.

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अध्याय 8: Continuity - EXERCISE 8.1 [पृष्ठ १७५]

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