Quadratic Interpolation Formula: Function & Examples

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Jasmine Grover

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Interpolation is considered as the estimation of an unknown quantity or data point between two known quantities. Interpolation is simple if the seasonality, trends and long term cycles are available. The concept can be shown in regression analysis and series analysis in statistics. Though the interpolation algorithm is available as an in-built function in computers/ calculators, its formula has significance if the tabular form is available. Also represents an introduction for a bigger application of finite differences.

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Key Takeaways: Quadratic Interpolation, Function, Extrapolation, Lagrange Interpolation, Statistics, Algorithm, Quadratic interpolant


Quadratic Interpolation

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Interpolation approaches are a common methods to the more general area of line search for 

Optimization. In quadratic interpolation, the critical value of a function is bracketed, and a quadratic interpolant is fitted to the arc contained in the interval. Following that, the interpolant is minimized, and a new interval is determined on the basis of relation of the minimizer to the actual endpoints of the interval. 

Quadratic Interpolation

Quadratic Interpolation

Interpolation is used to calculate the value of f(x) or a function of x from the known values of a function. If the values are known as x0 <....< xn and y0 = f(x0).....yn = f(xn) and x1 < x < xn, then the estimated values of f(x) are considered as interpolation. Similarly, if x > xn or x < x2 then the f(x) approximate value is known to be an extrapolation.

The video below explains this:

Quadratic Equations Detailed Video Explanation:

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Formula for Quadratic Interpolation

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There are lagrange interpolation formulas and linear interpolation formulas that are used in order to identify the unknown values of a specific set of data points. The linear interpolation formula is known as follows:

Formula for Quadratic Interpolation

Formula for Quadratic Interpolation

In addition, Lagrange interpolation formula is as follows:

In addition, Lagrange interpolation formula is as follows:


Examples of Quadratic Interpolation

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Interpolation helps to calculate the value of an unknown quantity between two known quantities. Similarly, polynomial interpolation is used to calculate the values between known data points. An example for interpolation is given as follows.

Consider a person who planted a tree and started measuring its height from day 1. He records the measure each day and on the fourth day decides to determine the height. The tabular data of the plant’s height is recorded below:

Days Height (mm)
1 0
3 4
5 8
7 12
9 16
11 20

Using the given data, one can determine the height of the plant on any random day. The height on day four is estimated as 6 mm. Also, with the data we can say that the plant grows in a linear pattern. The pattern shows a straight line and the height can be determined by plotting the data on a graph. In case the plant stops growing in a linear direction, then the pattern takes the form of a curve. Linear interpolation formula is an effective way to solve this mathematical problem.


Things to Remember

  • Interpolation is considered as the estimation of an unknown data point between two known quantities.
  • Interpolation concept can be expressed in regression analysis and series analysis in statistics.
  • The formula is used to determine the unknown values for any data related to geography such as elevation, rainfall, noise level, etc.
  • There are various types of interpolation methods such as biharmonic interpolation method, thin-plate spline method, cubic spline method, linear interpolation, etc.

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Sample Questions

Ques: Explain Lagrange interpolation formula? (2 marks)

Ans: Lagrange interpolation formula can be used to determine a polynomial known as Lagrange polynomial, which takes on specific values at arbitrary points. It is an nth degree polynomial approximation to f(x).

Ques: What is an interpolation? (2 marks)

Ans: Interpolation helps in calculating an unknown value that comes between known values. Suppose, a straight passes through two known points. Using the known values, we can estimate the point of the unknown value.

Ques: What are some advantages and disadvantages of Lagrange interpolation? (2 marks)

Ans: It is simple and easy to remember. The application of the formula is not swift. The disadvantage is that the chances of getting errors is high. Also, one cannot determine if the functional values used for the calculation are correct or not. 

Ques: Define linear interpolation? (2 marks)

Ans: Linear interpolation is used to calculate values at a point in between a given point. The points are conjoined by a simple line segment. Each segment can be interpolated individually. The values on the interrelated line can be estimated via the parameter mu. Linear interpolation is used to calculate the values of internet rate for a point or security in which no data is provided.

Ques: How to identify the interpolation between two numbers? (2 marks)

Ans: Consider the formula y = y1 + ((x – x1) / (x2 – x1)) * (y2 – y1). The known value is x and y is the unknown value. The coordinates below the known value x are x1 and y1. The coordinates above the x value are x2 and y2.

Ques: What produces smooth interpolation? (2 marks)

Ans: The smoother interpolants are being produced by polynomial interpolation and spline interpolation.

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CBSE CLASS XII Related Questions

  • 1.
    A line passing through the points \(A(1,2,3)\) and \(B(6,8,11)\) intersects the line \[ \vec r = 4\hat i + \hat j + \lambda(6\hat i + 2\hat j + \hat k) \] Find the coordinates of the point of intersection. Hence write the equation of a line passing through the point of intersection and perpendicular to both the lines.


      • 2.

        Sports car racing is a form of motorsport which uses sports car prototypes. The competition is held on special tracks designed in various shapes. The equation of one such track is given as 

        (i) Find \(f'(x)\) for \(0<x>3\). 
        (ii) Find \(f'(4)\). 
        (iii)(a) Test for continuity of \(f(x)\) at \(x=3\). 
        OR 
        (iii)(b) Test for differentiability of \(f(x)\) at \(x=3\). 
         


          • 3.
            Evaluate : \[ \int_{-\frac{\pi}{6}}^{\frac{\pi}{3}}(\sin|x|+\cos|x|)\,dx \]


              • 4.
                Find the sub–interval of \((0,\pi)\) in which the function \[ f(x)=\tan^{-1}(\sin x-\cos x) \] is increasing and decreasing.


                  • 5.

                    The probability of hitting the target by a trained sniper is three times the probability of not hitting the target on a stormy day due to high wind speed. The sniper fired two shots on the target on a stormy day when wind speed was very high. Find the probability that 
                    (i) target is hit. 
                    (ii) at least one shot misses the target. 


                      • 6.
                        If \[ P = \begin{bmatrix} 1 & -1 & 0 \\ 2 & 3 & 4 \\ 0 & 1 & 2 \end{bmatrix} \quad \text{and} \quad Q = \begin{bmatrix} 2 & 2 & -4 \\ -4 & 2 & -4 \\ 1 & -1 & 5 \end{bmatrix} \] find \( QP \) and hence solve the following system of equations using matrix method:
                        \[ x - y = 3,\quad 2x + 3y + 4z = 13,\quad y + 2z = 7 \]

                          CBSE CLASS XII Previous Year Papers

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