Evaluate the indefinite integral as an infinite series.
Can someone help me figure this out?
I'm pretty stuck.
Thanks!
arctan(x^5)dx
Can someone help me figure this out?
I'm pretty stuck.
Thanks!
arctan(x^5)dx
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d/dx [arctan(x)] = 1/(1 + x²)
1/(1 - x) = 1 + x + x² + x³ + ... + xⁿ
1/(1 - (-x)) = 1 - x + x² - x³ + ... + (-x)ⁿ
1/(1 + x²) = 1 - x² + x⁴ - x⁶ + ... + (-x²)ⁿ
Integrate both sides:
arctan(x) = x - x³/3 + x⁵/5 - x⁷/7 + ... + (-1)ⁿ x²ⁿ⁺¹ / (2n+1)
arctan(x⁵) = x⁵ - x¹⁵/3 + x²⁵/5 - x³⁵/7 + ... + (-1)ⁿ x¹⁰ⁿ⁺⁵ / (2n+1)
Write the integral:
∫ arctan(x⁵) dx = ∫ [x⁵ - x¹⁵/3 + x²⁵/5 - x³⁵/7 + ... + (-1)ⁿ x¹⁰ⁿ⁺⁵ / (2n+1)] dx
.................... = ∫ [Σ[n=0,∞] (-1)ⁿ x¹⁰ⁿ⁺⁵ / (2n+1)] dx
1/(1 - x) = 1 + x + x² + x³ + ... + xⁿ
1/(1 - (-x)) = 1 - x + x² - x³ + ... + (-x)ⁿ
1/(1 + x²) = 1 - x² + x⁴ - x⁶ + ... + (-x²)ⁿ
Integrate both sides:
arctan(x) = x - x³/3 + x⁵/5 - x⁷/7 + ... + (-1)ⁿ x²ⁿ⁺¹ / (2n+1)
arctan(x⁵) = x⁵ - x¹⁵/3 + x²⁵/5 - x³⁵/7 + ... + (-1)ⁿ x¹⁰ⁿ⁺⁵ / (2n+1)
Write the integral:
∫ arctan(x⁵) dx = ∫ [x⁵ - x¹⁵/3 + x²⁵/5 - x³⁵/7 + ... + (-1)ⁿ x¹⁰ⁿ⁺⁵ / (2n+1)] dx
.................... = ∫ [Σ[n=0,∞] (-1)ⁿ x¹⁰ⁿ⁺⁵ / (2n+1)] dx
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http://www.wolframalpha.com/in…
That's the correct series, then you just integrate it. Not sure what you want me to 'recheck', since Wolfram backs me up.
That's the correct series, then you just integrate it. Not sure what you want me to 'recheck', since Wolfram backs me up.
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