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Let a and b be nonzero real numbers. The coefficient of x⁵ in the expansion of (ax² + 70/(27bx))⁴ equals the coefficient of x^(-5) in the expansion of (ax - 1/(bx²))⁷. Find the value of 2b.
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Correct answer: 3
Solution
Matching the two coefficients by equating them yields a relationship between a and b from which 2b can be determined.
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