How is this C?
Given:
x^2+y^2 = 81 \tag{1}
x^2-y^2 =0\tag{2}
From eq 2
x^2=y^2\tag{3}
Now, if both x and y are the same then subtracting them would result in zero
1 Like
Alternatively, since we know that a^2-b^2 = (a+b)*(a-b), the expression x^4-y^4 can also be simplified into x^4-y^4 = (x^2 + y^2)*(x^2 - y^2) = 81*0 = 0.
3 Likes
ahhh, I didn’t see that! This makes complete sense, thank you.