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
Question 7
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
dxdy=−4yx.
This equation describes how the rate of change of y depends on x and y. The negative sign indicates that as x increases, y 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) is given by the equation.
When y>0, the slopes will be negative for positive x, indicating falling curves.
When y<0, the slopes will be positive for positive x, indicating rising curves.
The slopes approach zero as y 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>0 and positive for y<0 as x 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.