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We are given that $$\int \frac{dx}{x + x^7} = p(x)$$. We need to find $$\int \frac{x^6}{x + x^7} dx$$.
First, simplify the denominator in both integrals. Notice that $$x + x^7 = x(1 + x^6)$$. So, the given integral becomes:
$$p(x) = \int \frac{dx}{x(1 + x^6)}$$
Now, consider the integral we need to compute:
$$\int \frac{x^6}{x + x^7} dx = \int \frac{x^6}{x(1 + x^6)} dx$$
Simplify the fraction:
$$\frac{x^6}{x(1 + x^6)} = \frac{x^6}{x \cdot (1 + x^6)} = \frac{x^5}{1 + x^6}$$
So, the integral becomes:
$$\int \frac{x^5}{1 + x^6} dx$$
To relate this to $$p(x)$$, observe the expression for $$p(x)$$:
$$p(x) = \int \frac{dx}{x(1 + x^6)}$$
Consider the algebraic identity:
$$\frac{1}{x(1 + x^6)} = \frac{1}{x} - \frac{x^5}{1 + x^6}$$
Verify this by combining the terms on the right:
$$\frac{1}{x} - \frac{x^5}{1 + x^6} = \frac{1 + x^6 - x^6}{x(1 + x^6)} = \frac{1}{x(1 + x^6)}$$
This confirms the identity. Therefore, we can write:
$$p(x) = \int \left( \frac{1}{x} - \frac{x^5}{1 + x^6} \right) dx$$
Split the integral:
$$p(x) = \int \frac{1}{x} dx - \int \frac{x^5}{1 + x^6} dx$$
We know that $$\int \frac{1}{x} dx = \ln|x| + c_1$$, where $$c_1$$ is a constant. Let $$I = \int \frac{x^5}{1 + x^6} dx$$, so:
$$p(x) = \ln|x| - I + c_1$$
Solve for $$I$$:
$$I = \ln|x| - p(x) + c_1$$
But $$I$$ is exactly the integral we need, $$\int \frac{x^5}{1 + x^6} dx = \int \frac{x^6}{x + x^7} dx$$. Therefore:
$$\int \frac{x^6}{x + x^7} dx = \ln|x| - p(x) + c$$
where $$c = c_1$$ is the constant of integration.
Comparing with the options:
A. $$\ln|x| - p(x) + c$$
B. $$\ln|x| + p(x) + c$$
C. $$x - p(x) + c$$
D. $$x + p(x) + c$$
Option A matches our result.
Hence, the correct answer is Option A.
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