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Homogeneous & Linear Differential Equations · Question 20 of 120

Question 20

MediumOriginal question

F(x,y)F(x, y) is homogeneous of degree nn, F(1,2)=3F(1, 2) = 3 and F(3,6)=243F(3, 6) = 243. What is nn?

Options for question 20

Show the answer and explanation
CorrectNot quiteAnswer B

Correct answer: B

Explanation

  1. (3,6)=(3⋅1,3⋅2)(3, 6) = (3 \cdot 1, 3 \cdot 2), so F(3,6)=3nF(1,2)F(3, 6) = 3^{n}F(1, 2): 3n⋅3=2433^{n} \cdot 3 = 243.

  2. 3n=81=343^{n} = 81 = 3^{4}, so n=4n = 4.

Worth noting

5 reads 243=35243 = 3^{5} but forgets the factor F(1,2)=3F(1, 2) = 3.

Concept
A homogeneous function at \((\lambda x, \lambda y)\)
Typical time
90 s
Your time
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The rule this testsHomogeneous 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.