If 2a+3b=7 and ab =2, find 8a cube + 27b cube (give with full formula)
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as we know,
(x + y)³ = x³ + y³ + 3x²y + 3xy²
= x³ + y³ + 3xy(x + y)
(2a + 3b)³ = (2a)³ + (3b)³ + 3(2a)(3b)[2a + 3b]
(7)³ = 8a³ + 27b³ + 12ab(7)
343 = 8a³ + 27b³ + 12(2)(7)
343 = 8a³ +27b³ + 168
343 - 168 = 8a³ + 27b³
175 = 8a³ + 27b³
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