21 If a + 2b = 5, prove that a3 + 8b^3 + 30ab = 125.
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Answer:
proved
Step-by-step explanation:
(a+2b)=5
cube the equation
(2a+b)³=5³
(2a+b)(2a+b)²=125
a³+8b³+6a²b+12b²a=125
a³+8b³+6ab(a+2b)=125
a³+8b³+6ab(5)=125. because (a+2b)=5
a³+8b³+30ab=125
proved
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