Question

if 2a + 3b = 15 and ab = 10 find the value of 8a³+ 27b³

Answer 1

2a + 3b = 15
on cubeing both sides,
(2a +3b)³ =15³
(2a)³+(3b)³+3*2a*3b(2a+3b)=3375
8a³+27b³+18ab(15)=3375
8a³+27b³+18(10)[15]=3375
8a³+27b³+2700=3375
8a³+27b³=3375-2700=675
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