Newton–Raphson method is used to compute a root of the equation x2 + 5x − 10 =…

2021

Newton–Raphson method is used to compute a root of the equation x2 + 5x − 10 = 0 with 1 as the initial value. The approximate value after one iteration is _____.

  1. A.

    1.571

  2. B.

    0.429

  3. C.

    1.528

  4. D.

    1.429

Attempted by 7 students.

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Correct answer: A

We apply the Newton–Raphson iteration formula:

xₙ₊₁ = xₙ − f(xₙ) / f′(xₙ)

Here f(x) = x² + 5x − 10, so the derivative is f′(x) = 2x + 5.

Step 1 — Evaluate f and f′ at the initial value x₀ = 1:

f(1) = (1)² + 5(1) − 10 = 1 + 5 − 10 = −4

f′(1) = 2(1) + 5 = 7

Step 2 — Apply the formula for the first iteration:

x₁ = 1 − [ f(1) / f′(1) ] = 1 − (−4 / 7) = 1 + 4/7

x₁ = 1 + 0.5714… ≈ 1.571

Therefore, after one iteration the approximate root is 1.571 (rounded to three decimal places).

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