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# differential equation watch

1. hi, i'm not sure where the starred line has come from, can anyone help? thank you
2. You have an equation for involving , and you know that , so substitute the expression for in to eliminate it.
3. the RHS is just the same but subbing in the constant C and using log rules.
4. (Original post by Kolya)
You have an equation for involving , and you know that , so substitute the expression for in to eliminate it.
isn't c=1/2 - ln2 ?

i get

y^2/2 = ln(1+e^x) + 1/2 - ln2

which is close but not the same
5. (Original post by furryvision)
isn't c=1/2 - ln2 ?

i get

y^2/2 = ln(1+e^x) + 1/2 - ln2

which is close but not the same
You're correct for c.
Then use your laws of logs to combine the two log terms.
6. (Original post by Slumpy)
You're correct for c.
Then use your laws of logs to combine the two log terms.
fab thank you, there's so many rules/laws i need to learn in the next 2 weeks!
7. (Original post by furryvision)
fab thank you, there's so many rules/laws i need to learn in the next 2 weeks!
No worries.

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