Q. The equations x+y=3 and −5x−5y=−15 are graphed in the xy-plane. Which of the following must be true of the graphs of the two equations?
Analyze Equation: Analyze the first equation.The first equation is x+y=3. This is a linear equation in two variables and represents a straight line in the xy-plane.
Convert to Slope-Intercept: Put the first equation in slope-intercept form.To find the slope and y-intercept of the line represented by the first equation, solve for y: y=−x+3.
Analyze Second Equation: Analyze the second equation.The second equation is −5x−5y=−15. This is also a linear equation in two variables and represents a straight line in the xy-plane.
Simplify Second Equation: Simplify the second equation.Divide the entire second equation by −5 to simplify it: x+y=3.
Compare Simplified Equations: Compare the two simplified equations. After simplifying the second equation, we see that it is identical to the first equation: x+y=3.
Determine Relationship: Determine the relationship between the two graphs.Since both equations are identical after simplification, their graphs must be the same line in the xy-plane.
Conclude: Conclude the relationship between the two graphs.The graphs of the two equations are coincident lines, meaning they lie on top of each other in the xy-plane.
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