This is what I was given:

x+y=11

x² - y² = 77

I need to find x. How do I do this?

Do I square the x+y=11 and then add the two equations to find x?

Printable View

- Oct 2nd 2010, 07:40 PMjjkk5522Non-linear system of two equations
This is what I was given:

x+y=11

x² - y² = 77

I need to find x. How do I do this?

Do I square the x+y=11 and then add the two equations to find x? - Oct 2nd 2010, 07:44 PMEducated
Use the substitution method to solve this simultaneous equation.

Rewrite one of the equations as y=... and then substitute this into the second equation everytime y occurs. - Oct 2nd 2010, 07:51 PMspruancejr
Find out what x or y equals in one of the equations and then substitute it into the second equation. This gives you the value of one variable. Then just plug that value into one of the original equations to find the other variable:

EX:

x + y = 10

2y - 2x = 0

x = -y + 10

2y - 2(-y + 10) = 0

2y + 2y - 20 = 0

4y = 20

y = 5 - Oct 2nd 2010, 08:35 PMjjkk5522
so it should look like this?

y=-x+11

x²-(-x+11)²=77

x²+x²-121=77

2x²=198

x²=99

x is about 9.95?

but the real answer is supposed to be x=9.

what did i do wrong? - Oct 2nd 2010, 08:55 PMEducated
You expanded the brackets (-x+11)² wrong.

Remember: (a+b)² = a² * 2ab * b² - Oct 3rd 2010, 02:05 PMjjkk5522
Thank you for the help. I finally get it now.