Question

if 2x-5Y=2 and XY=12 find the value of 8x^3- 125y^3​

Answer 1

Step-by-step explanation:

2x - 5y = 2

xy = 12

x = 12/ y

2(12/y) - 5y = 2

on taking lcm

24 - 5y² =2y

5y² - 2y - 24 = 0

5y² -12y + 10y - 24 = 0

y ( 5y - 12 ) + 2 ( 5y -12 ) = 0

( y + 2) ( 5y - 12) = 0

y = - 2 or y = 12/5

putting in xy = 12

x = - 6 or x = 5

to find

8x³ - 125y³

8 ( - 6)³ - 125( - 2)³

8 × 216 + 1000

= - 728

or

8 (5)³ - 125 (12/5)³

1000 - 1728

- 728

Hence answer is always - 728