Solve simultaneously:
\(x+y=2\)
and
\(y+1={-3 \over x-1}\)
I did this:
\(x+y=2\)
\(x=2-y.....(1)\)
\(y+1={-3 \over x-1}.....(2)\)
(1) into (2)
\(y+1={-3 \over (2-y)-1}\)
\(y+1={-3 \over -2+y}\)
\((y+1)(y-2)=-3\)
\(y^2-y=-1\)
\(y(y-1)=-1\)
\(y=-1\) or \(y-1=-1\)
\(y=0\)
Then I substituted the y values into (1), getting the x values to be 3 and 2 respectively.
Then another question follows:
Hence, or otherwise, determine the value of:
\(({1 \over x}+{1 \over y})\)
The teacher says the answer should be \(-{1 \over4}\), I do not get that.
where did I go wrong?...please help..Thank you all very much indeed.
You're OK until here
y + 1 = - 3
_________
(2 - y) - 1
y + 1 = -3
______
1 - y
(1 + y) (1 - y) = - 3
-y^2 + 1 = - 3
-y^2 + 4 = 0 multiply through by -1
y^2 - 4 = 0
y^2 = 4
y = 2 or y = -2
So
x + 2 = 2 or x - 2 = 2
x = 0 x = 4
reject since 1/x isn't defined
So x = 4 , y = -2
1/4 + 1/-2 =
1/4 - 2/4 =
-1/4
CPhill,
I should have minused, not multiply!!...ooh dear me!!!..thank you CPhill!