Respuesta :

Answer is b. (-1, -5)
Step by step
Substitute the x and y values into both equations to find equality

Answer b. Makes both equations equal

2x + y = -7

2(-1) + (-5) = -7
-2 -5 = -7
-7 = -7
It equals now let’s do the 2nd one

x - y = 4
-1 -(-5) = 4
4 = 4
This one equals too. I did the math on the other three answers and they did not equal.

Problem solved!
eunice1234

Answer: B. (-1, -5)

Step-by-step explanation:

Given equations

2x + y = -7

x - y = 4

Concept

[tex]A^{-1}=\frac{1}{ad-bc}\left[\begin{array}{ccc}a&b\\c&d\\\end{array}\right][/tex]

[tex]A*A^{-1}=A^{-1}*A=I~(Which~is~basically~1)[/tex]

Convert into matrix

[tex]\left[\begin{array}{ccc}2&1\\1&-1\\\end{array}\right] \left[\begin{array}{ccc}x\\y\\\end{array}\right]=\left[\begin{array}{ccc}-7\\4\\\end{array}\right][/tex]

Calculate the inverse of the matrix

[tex]A=\left[\begin{array}{ccc}2&1\\1&-1\\\end{array}\right][/tex]

[tex]A^{-1}=\frac{1}{ad-bc}\left[\begin{array}{ccc}a&b\\c&d\\\end{array}\right][/tex]

[tex]A^{-1}=-\frac{1}{3} \left[\begin{array}{ccc}-1&-1\\-1&2\\\end{array}\right][/tex]

Solve by multiplying the inverse of the matrix

[tex]A*A^{-1}=A^{-1}*A=I[/tex]

[tex]-\frac{1}{3} \left[\begin{array}{ccc}-1&-1\\-1&2\\\end{array}\right]\left[\begin{array}{ccc}2&1\\1&-1\\\end{array}\right] \left[\begin{array}{ccc}x\\y\\\end{array}\right]=-\frac{1}{3} \left[\begin{array}{ccc}-1&-1\\-1&2\\\end{array}\right]\left[\begin{array}{ccc}-7\\4\\\end{array}\right][/tex]

[tex]1*\left[\begin{array}{ccc}x\\y\\\end{array}\right]=-\frac{1}{3}\left[\begin{array}{ccc}3\\15\\\end{array}\right][/tex]

Simplify by multiplication

[tex]\left[\begin{array}{ccc}x\\y\\\end{array}\right]=\left[\begin{array}{ccc}-1\\-5\\\end{array}\right][/tex]

Therefore, the answer is [tex]\Large\boxed{(-1,~-5)}[/tex]

Hope this helps!! :)

Please let me know if you have any questions

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