If x+y=7 and x-y =3,then x ²-y ²=

A -4

B 4

C 10

D 21

Correct Answer: Option D

দেওয়া আছে ,
        x+y=7
এবং x-y=3
অতএব, x ²-y ²=(x+y)( x-y)
                       =7×3
                        =21