Question

if x -y =5 and xy = 84 find x3 -y3
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Answer 1

X-Y=5

X=5+Y ---------->Equation I

XxY=84---------> II

Putting the value of X in equation II

(5+Y)xY=84

Y^2+5Y=84

Y^2+5Y-84=0

Y^2+12Y-7Y-84=0

Y(Y+12)-7(Y+12)=0 (quadratic form)

(Y+12)(Y-7)=0 (zero product rule)

Y=7

then X =12 (putting value of Y in any equation)

X^3-Y^3

=12^3-7^3

=1728-343

=1385

I was not sure if you had to find x cube - y cube

or

x into 3 - y into 3