A Closer Look at Coinciding Lines

In the previous post, we have asked a question about coinciding lines. We observed that the lines with equations 3x + 8y = 12 and 6x + 16y = 24 coincide. It is not difficult to see that 6x + 16y = 24 is 2(3x + 8y = 12). The question now is if one equation is a multiple of the other, are their graphs coinciding? We answer this question below.

Consider a point with coordinates (2,3). What happens if we multiply the coordinates by 2, 3, and 4? If we do this, the coordinates become (4, 6), (6,9), and (8,12). Now, what is so special about these points? As we can see in the graph below, they lie on the same line. Can you explain why?  » Read more

On Equations of Intersecting, Coinciding, and Parallel Lines

When we have two lines on a plane, there are three possibilities:

  • the lines will never meet (parallel)
  • the lines will meet at one point (intersecting)
  • the lines will meet at infinitely many points (coinciding).

As for the third case, coinciding means that lines which are on top of each other.

In Algebra, we have learned that a line can be represented with an equation. The equations which represent lines are called linear equations. We have learned that linear equations can be represented by y = mx + b, where m and b are real numbers.

We can examine the three cases mentioned above in terms of equations. Can we determine if lines are parallel, intersecting, or coinciding based on equations only?  » Read more

How to Represent Inequalities in One Variable

The inequality x > 3 means all numbers greater than 3. The set of numbers that makes the inequality true is called the solution set of the inequality. An instance of this numbers such as 4 is a solution to x > 3.

The graph of x > 3 is shown on the number line below. The “empty circle” means that the solution does not include 3. The highlighted part of the number line (blue ray) means that it includes all real numbers greater than 3 and the arrow indicates that it goes up to infinity.

representing inequalities

Another notation to represent x > 3 is (3, ∞). The number on the left side is the lower bound and the right side is the upper bound. This notation means from 3 up to infinity. In addition, the symbol ( denotes that 3 is not included in the solution. Therefore, the interval (5,7) means all real numbers from 5 to 7, not including 5 and 7. The infinity symbol always takes the ( and ) symbols.  » Read more

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