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 _____.
- A.
1.571
- B.
0.429
- C.
1.528
- 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).