Question

6. without actually calculating the value (28)³+ (-15) ³+ (-13)³
(a) 16380
(b) -16380. (c) 15380
(d) - 15380​

Answer 1

Answer:

(b)  -16380

Step-by-step explanation:

Let a=28

     b=-15

     c=-13

$a^{3}+bx^{3} +c^{3} =(a+b+c)(a^{2} +b^{2} +c^{2} -ab-bc-ca)-3abc$

$28^{3}+( -15)^{3}+( -13)^{3}\\\\ =(28-15-13)(28^2 +15^2 +13^2-28*15-15*13*28*13) -3*28*(-15)*(-13)$

$=0-3*28*(-15)*(-13)\\\\=0-16380\\\\=-16380$