Question

Find the value of 64a3 + 125b3 if 4a + 5b = 5 and ab = −1.

Answer 1

Answer:

140

Step-by-step explanation:

64a^3 + 125b^3  =  (4a)^3 + (5b)^3

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

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

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

so,

64a^3 + 125b^3 = (5)((a+b)^2 - 2ab - ab)

= 5((5)^2 - 3ab)

=5(25 - 3(-1))

= 5(25+3)

= 5(28)

= 140

Hope this helps you...

Answer 2

Here is the correct answer