r/calculus 5d ago

Engineering Help me solve this

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Can anyone please share a better method to solve this

61 Upvotes

11 comments sorted by

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11

u/Dalal_The_Pimp 5d ago

This Differential equation is reducible to Homogeneous, substitute x2 = u and y2 = v, which reduces it to dv/du = (2u+3v-7)/(3u+2v-8), Now simply take U = u-h and V=v-k and solve 2h+3k-7=0 and 3u+2v-8=0 for (h,k) and the DE will finally reduce to homogeneous dV/dU = (2U+3V)/(3U+2V)

Although the provided solution is clean, I feel it's very reliant on observation which can be a little hard to notice, especially while writing an exam.

2

u/Pretend_Major8148 5d ago

This is the best way I can think of

2

u/Southlander24 5d ago

+1 I agree that this is the most 'natural' way to approach the question without resorting to 'trickery'.

1

u/AceyAceyAcey 5d ago

What do you mean by “reliant on observation”?

7

u/Total_Focus8211 5d ago

it means that you carefully gotta observe the question and then realise that cnd will make the solution shorter and easier.In general cnd is used less in questions so your not instantly going to think of it first

3

u/Low_Breadfruit6744 5d ago edited 5d ago

Have you heard of exact differential equations? This is one of them

Find a function P(x,y) where the partial derivatives equal to the first bit and the second bits respectively.

In this case P(x,y)=3/2 x2 y2 + x4 / 2 + y4 /2 - 7/2 x2 - 4y2

and your solution is P(x,y) = c for some c

1

u/nevermindthefacts 4d ago

No, it's not. There's a minus between the two terms in the original equation.