1.

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

Answer»

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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