Decide which ordered pair is a solution of the system

Question

2x-3y=4

x+4y=-9

 

A) (1, -2) 

B) (-1,-2)

C) (-1, 2)

D) (1, 2)

Answer 1

Another method you can use for this one is the substitution method.

 

2x - 3y = 4               eq1
x + 4y = -9              eq2

 

 

Notice that we can solve for x from eq2, since the coefficient is 1.

 

x = -4y - 9

 

 

Substitute this value of x into eq1.  This will allow use to obtain an equation only one variable.

 

2(-4y - 9) - 3y = 4

 

-8y - 18 - 3y = 4

 

-11y - 18 = 4

-11y = 22

     y = -2

 

Since your y value is -2, we can eliminate choices C and D.

 

 

Now substitute the value of y into eq2.

 

x = -4y - 9

x = -4(-2) - 9

x = 8 - 9

x = -1

 

The ordered pair is (-1, -2).

 

Your answer is (B).

Answer 2

 2X - 3Y = 4

-2X - 8Y = 18  (Multiplying the second equation by -2 all the way across

-----------------

 0X -11y = 22 (adding the two equations)

 

Y = -2

Putting Y into the first equation and solving for X gives

X = -1

So the ordered pair is

(-1, -2) or B