# calculus

Integrate: dx/(2x^2 + 4x + 7)

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1. messy, are you sure you typed correctly?
I was hoping the bottom would factor so I could use partial fractions.

the way it stands I ran it through an integration program to get

(√10/10)[tan -1 [√10(x+1)/5]

are you working at that sophisticated level of integration??
Is this highschool level ??

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posted by Reiny
2. You can just write the denominator as:

2x^2 + 4x + 7 =

2 (x^2 + 2 x + 7/2) =

2 [(x + 1)^2 + 5/2]

Then you use the fact that the integral of dx/(x^2 + a^2) = 1/a arctan (x/a)

So, the integral is:

1/2 1/sqrt(5/2) arctan[(x+1)/sqrt(5/2)]=

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posted by Count Iblis
3. Thanks Reiny + Iblis!

This is from Wiley textbook "Calculus: Early Transcendentals Combined, 8th Edition", section 8.4. I think problem #41 (from memory).

I typed it right. The answer you two wrote matches the book, however I couldn't figure out how to do it. Makes sense now. Thanks

Reiny, thanks for writing that. I feel like an idiot getting stuck on these textbook problems sometimes.

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posted by mathstudent

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