jlgdr wrote:
If x+y=a and x-y=b, then 2xy=?
a) \(\frac{(a^2 - b^2)}{2}\)
b) \(\frac{(b^2 - a^2)}{2}\)
c) \(\frac{(a - b )}{2}\)
d) \(\frac{(ab)}{2}\)
e) \(\frac{(a^2 + b^2)}{2}\)
Squaring the first equation, we have:
x^2 + 2xy + y^2 = a^2
Squaring the second equation, we have:
x^2 - 2xy + y^2 = b^2
Subtracting the second equation from the first, we have:
4xy = a^2 - b^2
2xy = (a^2 - b^2)/2
Answer: A
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81% (01:13) correct 
