Question
If 4x + 1/5x = 4, then find value of 125x³ +
1/64x³?Solution
4x + 1/5x = 4 By multiplying 5/4 , 4x × 5/4 + 1/5x × 5/4 = 4 × 5/4 5x + 1/4x = 5 On cubing both the sides, (5x+1/4x)^3 = (5)³ = 125x³ + 1/64x³ + 3 × 5x × 1/4x (5x+1/4x) = 125 = 125x³ + 1/64x³ + (3×5)/4 × 5 = 125 = 125x³ + 1/64x³ + 75/4 = 125 = 125x³ + 1/64x³ = 125 - 75/4 = 125x³ + 1/64x³ = (500-75)/4 = 125x³ + 1/64x³ = 425/4
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