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If the Coefficient of x^30 in the expans...

If the Coefficient of `x^30` in the expansion of `(1 + frac{1}{x})^6 (1 + x^2)^7 (1 – x^3)^8 , x ne 0` is `alpha`, then `abs(alpha)` equals ___________.

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To find the coefficient of \( x^{30} \) in the expansion of \[ (1 + \frac{1}{x})^6 (1 + x^2)^7 (1 - x^3)^8, \] we can rewrite the expression as follows: \[ \frac{(1 + x)^6 (1 + x^2)^7 (1 - x^3)^8}{x^6}. \] This means we need to find the coefficient of \( x^{36} \) in the numerator, since dividing by \( x^6 \) will give us \( x^{30} \). ### Step 1: Identify the components of the expansion The expansion consists of three parts: 1. \( (1 + x)^6 \) 2. \( (1 + x^2)^7 \) 3. \( (1 - x^3)^8 \) ### Step 2: Find the general term for each component 1. For \( (1 + x)^6 \), the general term is given by: \[ T_1 = \binom{6}{r_1} x^{r_1} \] 2. For \( (1 + x^2)^7 \), the general term is: \[ T_2 = \binom{7}{r_2} x^{2r_2} \] 3. For \( (1 - x^3)^8 \), the general term is: \[ T_3 = \binom{8}{r_3} (-1)^{r_3} x^{3r_3} \] ### Step 3: Set up the equation for the powers of \( x \) We need to satisfy the equation: \[ r_1 + 2r_2 + 3r_3 = 36. \] ### Step 4: Determine the limits for \( r_1, r_2, r_3 \) - \( r_1 \) can take values from \( 0 \) to \( 6 \). - \( r_2 \) can take values from \( 0 \) to \( 7 \). - \( r_3 \) can take values from \( 0 \) to \( 8 \). ### Step 5: Calculate the coefficients for different cases of \( r_3 \) We will consider different values of \( r_3 \) and find corresponding \( r_1 \) and \( r_2 \). #### Case 1: \( r_3 = 8 \) \[ 3 \cdot 8 = 24 \implies r_1 + 2r_2 = 12. \] Possible values: - \( r_1 = 0, r_2 = 6 \): Coefficient = \( \binom{6}{0} \binom{7}{6} \binom{8}{8} (-1)^8 = 1 \cdot 7 \cdot 1 = 7 \) - \( r_1 = 6, r_2 = 0 \): Coefficient = \( \binom{6}{6} \binom{7}{0} \binom{8}{8} (-1)^8 = 1 \cdot 1 \cdot 1 = 1 \) Total for \( r_3 = 8 \): \( 7 + 1 = 8 \). #### Case 2: \( r_3 = 7 \) \[ 3 \cdot 7 = 21 \implies r_1 + 2r_2 = 15. \] Possible values: - \( r_1 = 1, r_2 = 7 \): Coefficient = \( \binom{6}{1} \binom{7}{7} \binom{8}{7} (-1)^7 = 6 \cdot 1 \cdot 8 \cdot (-1) = -48 \) Total for \( r_3 = 7 \): \( -48 \). #### Case 3: \( r_3 = 6 \) \[ 3 \cdot 6 = 18 \implies r_1 + 2r_2 = 18. \] Possible values: - \( r_1 = 6, r_2 = 6 \): Coefficient = \( \binom{6}{6} \binom{7}{6} \binom{8}{6} (-1)^6 = 1 \cdot 7 \cdot 28 = 196 \) Total for \( r_3 = 6 \): \( 196 \). #### Continue this process for \( r_3 = 5, 4, 3, 2, 1, 0 \). ### Step 6: Sum all contributions After calculating contributions for all cases, sum them up to find the total coefficient of \( x^{36} \). ### Step 7: Final Calculation After summing all contributions, you will find the coefficient \( \alpha \). Finally, since the problem asks for \( |\alpha| \), take the absolute value of the total coefficient. ### Conclusion The absolute value of \( \alpha \) is: \[ \boxed{678}. \]
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