Question

If a + b =10 and 3/7 of ab = 9,then the value of $a^3+b^3=?$

• A. 270
• B. 370
• C. 200
• D. 142

Answer 1

Answer:

B. 370

$a^3+b^3=(a+b)(a^2-ab+b^2)$

$3/7\times{ab}=9$

$\implies{ab}={9\times7}/3=21$

$(a+b)^2=a^2+2ab+b^2$

$10^2=a^2+b^2+2\times21$

$a^2+b^2=100-42=58$

$a^3+b^3=(10)(58-21)$

$=370$