Back to Topic 5.18 — Differential equations (HL only)
5.18.3Math AA HL8 flashcards

Euler's method

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Card 1 of 85.18.3
5.18.3
Question

State Euler's method for dy/dx = f(x, y).

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All 8 Flashcards — Euler's method

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Card 1formula

Question

State Euler's method for dy/dx = f(x, y).

Answer

x_(n+1) = x_n + h, y_(n+1) = y_n + h·f(x_n, y_n), where h is the step size.

Card 2concept

Question

What does Euler's method actually do geometrically?

Answer

Follows the tangent (gradient f) in small straight steps of length h, approximating the curve by line segments.

Card 3concept

Question

Why is Euler's method only an approximation?

Answer

It uses the gradient at the START of each step, so it drifts off a curving solution; error grows with step size h.

Card 4concept

Question

If the solution curve is concave up, does Euler over- or under-estimate?

Answer

Underestimate — the tangents lie below a concave-up curve.

Card 5concept

Question

If the solution curve is concave down, does Euler over- or under-estimate?

Answer

Overestimate — the tangents lie above a concave-down curve.

Card 6formula

Question

How do you find the error of an Euler estimate?

Answer

error = |y_exact − y_Euler|, when the exact solution is known.

Card 7concept

Question

What happens to the error if you halve the step size h?

Answer

It roughly halves (error ∝ h), but you need twice as many steps.

Card 8concept

Question

Which paper most often features Euler's method?

Answer

Paper 3 (the extended-investigation paper), though it also appears in Paper 2.

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