If x^2-y^2=77 and x+y=11, what is the value of x?
I don't get why the correct answer is 9. Thanks in advance
I'll show you how I would do (and I guess it's faster...)
Divide by 11 :
And we had x+y=11.
Add these two equations term by term, because you have -y and y.
This gives (x-y)+(x+y)=7+11
Do you see which steps look simpler ?