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Sagot :

Answer:  Choice C

(-19/2, -33/2)

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Explanation:

We'll plug the second equation into the first one

In other words, we'll replace every copy of y with 3x+12 and solve for x

This is an example of the substitution rule.

x-y = 7

x-( y ) = 7

x - (3x+12) = 7

x - 3x - 12 = 7

-2x - 12 = 7

-2x = 7+12

-2x = 19

x = -19/2

Based on this alone, we can see the answer must be choice C. No other answer choice has this x coordinate.

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If you want to find y based on this x value, then,

y = 3x+12

y = 3(-19/2)+12

y = -57/2 + 12

y = -57/2 + 24/2

y = (-57+24)/2

y = -33/2

This fully confirms choice C is correct.

So we have x = -19/2 and y = -33/2 pair up to get us (-19/2, -33/2)

In decimal form, this would be (-9.5, -16.5)

Answer:

3. (-19/3, -33/2)

You have to make a equation system :

[tex]\left \{{{x - y = 7} \atop { y = 3x + 12}} \right. <=> \left \{{{y = x - 7} \atop { y = 3x + 12}} <=> x-7 = 3x + 12 <=> 3x -x = -7 - 12 <=>[/tex] [tex]2x = -19 <=> x = -19/2[/tex]

Replacing x=-19/2 in the first equation (it's the easiest to solve) :

[tex]y = -19/2 - 7 <=> y =-19/2- 14/2 <=> y = -33/2[/tex]