S Sarah2391 New member Joined Nov 28, 2007 Messages 26 Jan 13, 2008 #1 If (x+y)squared = 100 and (x-y)squared = 16, what is the value of xy? (a) 14 (b) 21 (c) 121 (d) 1600 (e) 64 How to solve?
If (x+y)squared = 100 and (x-y)squared = 16, what is the value of xy? (a) 14 (b) 21 (c) 121 (d) 1600 (e) 64 How to solve?
pka Elite Member Joined Jan 29, 2005 Messages 11,978 Jan 13, 2008 #2 Re: Help!! \(\displaystyle \begin{array}{l} x^2 + 2xy + y^2 = 100 \\ x^2 - 2xy + y^2 = 16 \\ \end{array}\) Substract the second from the first.
Re: Help!! \(\displaystyle \begin{array}{l} x^2 + 2xy + y^2 = 100 \\ x^2 - 2xy + y^2 = 16 \\ \end{array}\) Substract the second from the first.
S Sarah2391 New member Joined Nov 28, 2007 Messages 26 Jan 13, 2008 #3 Re: Help!! Thank you! Now I remember the formula
S Sarah2391 New member Joined Nov 28, 2007 Messages 26 Jan 13, 2008 #4 Re: Help!! Just to check, what did you get as the value of xy?
L Loren Senior Member Joined Aug 28, 2007 Messages 1,298 Jan 13, 2008 #6 Taking the square root of both sides of both given equations yields... x+y=+/-10 x-y=+/-4 This leads to (7,3), (-7,-3), (3,7), or (-3,-7). Therefore xy=what?
Taking the square root of both sides of both given equations yields... x+y=+/-10 x-y=+/-4 This leads to (7,3), (-7,-3), (3,7), or (-3,-7). Therefore xy=what?
