Question

if 2a + b equal to 12 and ab equal to 15 then the value of 8 a cube plus b cube = ? only a genius can answer this​

Answer 1

Hope this helps you thankyou for asking me the question and would help you if you have anymore doubt

Answer 2

$8a^{3} + b^{3} = 648$

Step-by-step explanation:

Given that, $2a + b = 12$

                   $ab = 15$

we know that, ${(a + b)}^{3} = a^{3} + b^{3} + 3ab(a + b)$

                            ${(2a + b)}^{3} = (2a)^{3} + b^{3} + 3(2a)b(2a + b)$

                     ⇒   ${(2a + b)}^{3} = 8a^{3} + b^{3} + 6ab(2a + b)$

                     ⇒   ${(12)}^{3} = 8a^{3} + b^{3} + 6\times 15 \times 12$

                     ⇒   ${1728 = 8a^{3} + b^{3} + 1080$

                     ⇒   $8a^{3} + b^{3} = 1728 -1080$

                     ⇒   $8a^{3} + b^{3} = 648$.