<p>I know most of you will think this is beyond easy but its driving me nuts. Please explain this to me so I can sleep tonight....</p>
<p>If x+y=6 and x-y=10 then x2-y2 = ??</p>
<p>the x2-y2 should be suprascript 2's </p>
<p>Thanks!</p>
<p>You have to add those two equations</p>
<p>x+y=6
x-y=10</p>
<p>You add them to get 2x=16, x=8. Plug 8 back into the first equation to get Y=-2. So then x^2-y^2= 64-4=60.</p>
<p>ok - I can follow the first part with -2 but I'm having trouble with the last part. Can you explain - So then x^2-y^2= 64-4=60</p>
<p>thanks</p>
<p>Got it - thanks again!!!!</p>
<p>Another way is to recognize that its difference of 2 squares. So x^2-y^2 factors into (x+y)(x-y)=(6)(10)=60</p>
<p>jaygatz121 - perfect.
A very useful formula for the SAT.</p>