The 2nd approximation to a root of the equation x2 - x - 1 = 0 in the interval (1, 2) by Bisection method will be:

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  1. 1.75
  2. 1.35
  3. 1.25
  4. 1.5

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Option 1 : 1.75
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Concept:

Bisection method:

Used to find the root for a function. Root of a function f(x) = a such that f(a)= 0

Property: if a function f(x) is continuous on the interval [a…b] and sign of f(a) ≠  sign of f(b). There is a value c belongs to [a…b] such that f(c) = 0, means c is a root in between [a….b]

Note:

Bisection method cut the interval into 2 halves and check which half contains a root of the equation.

1) Suppose interval [a…b] .

2) Cut interval in the middle to find m : \(m =\frac{{a+b}}{{2}}\)

3) sign of f(m) not matches with f(a) proceed the search in the new interval.

Calculation:

Given:

f(x) = x2 - x - 1 = 0  , a = 1 , b = 2

f(1) = 1 - 1 -1 = -1 < 0 , f(2) = 2- 2 - 1 = 1 > 0 , Hence root lies between 1 and 2

By Bi-section method, \(x_0 = \frac{{a+b}}{{2}} = \frac{3}{2}\)

\(f(x_0) =\frac{9}{4}-\frac{3}{2}-1=-\frac{1}{4}<0\)

Which is positive. Hence, the root lies between 1.5 and 2

By Bi-section method, \(x_1 = \frac{{2+1.5}}{{2}} = 1.75\)

The 2nd approximation to a root of the equation x2 - x - 1 = 0 in the interval (1, 2) by Bisection method is 1.75

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