If 2a - 3b = 3 and ab = 2,find the value of 8a cube - 27 b cube
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138
2a - 3b = 3
on cubing both side
(2a - 3b)³ = 3³
=> 8a³ - 27b³ - 3(2a)(3b)(2a - 3b) = 27
=> 8a³ - 27b³ - 18(2) (3) = 27
=> 8a³ - 27b³ = 27 + 108
=> 8a³ - 27b³ = 135
on cubing both side
(2a - 3b)³ = 3³
=> 8a³ - 27b³ - 3(2a)(3b)(2a - 3b) = 27
=> 8a³ - 27b³ - 18(2) (3) = 27
=> 8a³ - 27b³ = 27 + 108
=> 8a³ - 27b³ = 135
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17
Answer:
ex 3.2 expansion
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