How do you solve the following system?: −x−2y=1,9x−y=−1

1 Answer
Sittun Swayam P.
Nov 14, 2015

We can solve this question by finding the value of x with respect to y from both equations. Since the value of x should be equal, the equations thus obtained can be solved for y. And then either of the initial equations can be used to find x.

Explanation:

  1. −x−2y = 1 => −x=1+2y => x=−(1+2y) ----EQUATION 1
  2. 9x−y=−1 => 9x=y−1 => x=19⋅(y−1) ----EQUATION 2

Equating the values of x from EQUATION 1 and EQUATION 2;
we have;
−(1+2y)=19⋅(y−1)
=> −9−18y=y−1
=>−18y−y=−1+9
=>−19y=8
=>y=−819

Using EQUATION 1;
x=−(1+2y)
=>x=−(1+2⋅(−819))
=>x=−(1−1619)
=>x=−319

So there you have it!!

x=−319
and
y=−819

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