What is the value of X^2 -Y^2?
I understand how 2 is sufficent but I am confused about stem 1 because the answer, according to the key, is D...
agreed that its D but its not a good question.
x = y. so x^2-y^2 = 0. suff.
x = -y. x and y have same values but just opposite signs. since squaring these variables eliminates the sign problems and gives x^2-y^2 = 0. also suff.