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without building the graph, find the coordinates of the point of intersection of the lines given by the equation y=3x-1 and 3x+y=-7

User Asif Jalil
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1. Determining the value of x and y:

Given equation(s):


  • y = 3x - 1

  • 3x + y = -7

To determine the point of intersection given by the two equations, it is required to know the x-value and the y-value of both equations. We can solve for the x and y variables through two methods.

Method-1: Substitution method

Given value of the y-variable: 3x - 1

Substitute the given value of the y-variable into the second equation to determine the value of the x-variable.


\implies 3x + y = -7


\implies3x + (3x - 1) = -7


\implies3x + 3x - 1 = -7

Combine like terms as needed;


\implies 3x + 3x - 1 = -7


\implies 6x - 1 = -7

Add 1 to both sides of the equation;


\implies 6x - 1 + 1 = -7 + 1


\implies 6x = -6

Divide 6 to both sides of the equation;


\implies (6x)/(6) = (-6)/(6)


\implies x = -1

Now, substitute the value of the x-variable into the expression that is equivalent to the y-variable.


\implies y = 3(-1) - 1


\implies
\ \ = -3 - 1


\implies
= -4

Therefore, the value(s) of the x-variable and the y-variable are;


\boxed{x = -1}
\boxed{y = -4}

Method 2: System of equations

Convert the equations into slope intercept form;


\implies\left \{ {{y = 3x - 1} \atop {3x + y = -7}} \right.


\implies \left \{ {{y = 3x - 1} \atop {y = -3x - 7}} \right.

Clearly, we can see that "y" is isolated in both equations. Therefore, we can subtract the second equation from the first equation.


\implies \left \{ {{y = 3x - 1 } \atop {- (y = -3x - 7)}} \right.


\implies \left \{ {{y = 3x - 1} \atop {-y = 3x + 7}} \right.

Now, we can cancel the "y-variable" as y - y is 0 and combine the equations into one equation by adding 3x to 3x and 7 to -1.


\implies\left \{ {{y = 3x - 1} \atop {-y = 3x + 7}} \right.


\implies 0 = (6x) + (6)


\implies0 = 6x + 6

This problem is now an algebraic problem. Isolate "x" to determine its value.


\implies 0 - 6 = 6x + 6 - 6


\implies -6 = 6x


\implies -1 = x

Like done in method 1, substitute the value of x into the first equation to determine the value of y.


\implies y = 3(-1) - 1


\implies y = -3 - 1


\implies y = -4

Therefore, the value(s) of the x-variable and the y-variable are;


\boxed{x = -1}
\boxed{y = -4}

2. Determining the intersection point;

The point on a coordinate plane is expressed as (x, y). Simply substitute the values of x and y to determine the intersection point given by the equations.

⇒ (x, y) ⇒ (-1, -4)

Therefore, the point of intersection is (-1, -4).

Graph:

without building the graph, find the coordinates of the point of intersection of the-example-1
User Aviv Goldgeier
by
8.0k points

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