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Homogeneous & Linear Differential Equations · Question 44 of 120

Question 44

MediumOriginal question

Which of these lines through the origin is a solution of dydx=2x2+y23xy\frac{dy}{dx} = \frac{2x^{2} + y^{2}}{3xy}?

Options for question 44

Show the answer and explanation
CorrectNot quiteAnswer A

Correct answer: A

Explanation

  1. On y=mxy = mx, dydx=m\frac{dy}{dx} = m and the right side is 2+m23m\frac{2 + m^{2}}{3m}; the line is a solution when these are equal.

  2. 2+m2=3m22 + m^{2} = 3m^{2} gives m2=1m^{2} = 1, so y=xy = x (and y=−xy = -x) are solutions.

Worth noting

y=2xy = 2x solves 2+m2=3m2 + m^{2} = 3m, which forgets to multiply the mm on the right by 3m3m.

Concept
Straight-line solutions of a homogeneous equation
Typical time
90 s
Your time
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The rule this testsSolving homogeneous equations
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Ten questions from Homogeneous & Linear Differential Equations, at your own pace.

Practise this chapter →

Ten questions from Homogeneous & Linear Differential Equations, at your own pace.