Question

if x-y=4,xy=21, find x³-y³​

Answer 1

Given, x−y=4 and xy=21                         

(x−y)2=42

⇒x2+y2−2xy=16

⇒x2+y2−2×21=16             

⇒x2+y2=16+42=58

Now, x3−y3=(x−y)(x2+y2+xy)

                        =(4)(58+21)=316      

the answer is 316

hope it helped you bro :)

have a nice day

#HPpatcher

Answer 2

Step-by-step explanation:

Given, x−y=4 and xy=21 ...(i)

(x−y)

2

=4

2

⇒x

2

+y

2

−2xy=16

⇒x

2

+y

2

−2×21=16 (from (i))

⇒x

2

+y

2

=16+42=58

Now, x

3

−y

3

=(x−y)(x

2

+y

2

+xy)

=(4)(58+21)=316