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Which of the following best represents the direction field for the differential equation $$\frac{dy}{dx} = -\frac{x}{4y}$$? A - HSC - SSCE Mathematics Extension 1 - Question 7 - 2020 - Paper 1

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Which-of-the-following-best-represents-the-direction-field-for-the-differential-equation-$$\frac{dy}{dx}-=--\frac{x}{4y}$$?--A-HSC-SSCE Mathematics Extension 1-Question 7-2020-Paper 1.png

Which of the following best represents the direction field for the differential equation $$\frac{dy}{dx} = -\frac{x}{4y}$$? A. B. C. D.

Worked Solution & Example Answer:Which of the following best represents the direction field for the differential equation $$\frac{dy}{dx} = -\frac{x}{4y}$$? A - HSC - SSCE Mathematics Extension 1 - Question 7 - 2020 - Paper 1

Step 1

Evaluate the Differential Equation

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Answer

The differential equation given is dydx=x4y\frac{dy}{dx} = -\frac{x}{4y}. This equation describes how the rate of change of yy depends on xx and yy. The negative sign indicates that as xx increases, yy tends to decrease.

Step 2

Determine the Characteristics of the Direction Field

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Answer

To sketch the direction field, we need to understand that the slope of the solution curves at any point (x,y)(x, y) is given by the equation.

  • When y>0y > 0, the slopes will be negative for positive xx, indicating falling curves.
  • When y<0y < 0, the slopes will be positive for positive xx, indicating rising curves.
  • The slopes approach zero as yy approaches zero.

Step 3

Compare with Options A, B, C, and D

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Answer

Observing the provided graphs:

  • Graph A shows the slopes consistent with the described behavior: negative for y>0y > 0 and positive for y<0y < 0 as xx increases.
  • The other graphs do not properly reflect the characteristics outlined, as their direction fields do not match well with the expected behavior of the slopes.

Step 4

Conclusion

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Answer

Therefore, the correct option that best represents the direction field for the given differential equation is A.

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