Question

if x-y=5 and xy=84 find the value of x cube - y cube​

Answer 1

Step-by-step explanation:

x-y=5. xy=84

x=5+y

do it by substitution method.

Answer 2

x-y=5

X=5+y

xy=84

(5+y)y=84

5y+ysquare =84

Y^2+5y-84=0 (factorise)

Y^2+12y-7y-84

Y(y+12)-7(y+12)

Y-7=0 y=7

Y+12=0 y=-12(this is negative)

So, y=7

x-y=5

x=5+7=12

x^3-y^3

12^3-7^3

1728-343=1385