Question

if 2a + b = 6, then show that 8a³ +b³ + 36ab = 216​

Answer 1

Answer:

∆Given equation: 2a+b=6

L.H.S=8a³+b³+36ab

=(2a)³+b³+36ab

=(2a+b)³-3×2a×b(2a+b)+36ab[Read at last for formula)

=(6)³-6ab×6+36ab

=216-36ab+36ab

=216[36ab plus and minus cancel out]=R.H.S(Proved)

At last I say you the formula,

♦a³+b³=(a+b)(a²-ab+b²) and it have also a formula

♦=(a+b)³-3ab(a+b)