If x+2y=a , and x-2y=b, which of the following is an expression for xy?
A)2(a+b/a-b)
b)2(a-b/a+b)
c)1
d)non
A)2(a+b/a-b)
b)2(a-b/a+b)
c)1
d)non
Need to point out that usually there are 5 choices in the test. None is usually (E). Also double check if the question asks xy or x/y.Hmna wrote:If x+2y=a , and x-2y=b, which of the following is an expression for xy?
A)2(a+b/a-b)
b)2(a-b/a+b)
c)1
d)non
x+2y = a
x-2y = b
Add equations:
==> x=(a+b)/2
Subtract equations
==> y = (a-b)/4
xy = (a^2-b^2)/8
