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Linear Equations in Two Variables

Two lines and one shared spot

Draw both equations on one grid. Where do the two lines cross? Tap the crossing.

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A grid, ready for both claims.
Step 1 of 4
  1. A grid, ready for both claims.
  2. Line 1: 2x + 3y = 12, through (0, 4) and (6, 0).
  3. Line 2: x − y = 1, through (1, 0) and (0, −1).
  4. They cross at (3, 2), the solution of the pair.

The rule

The lines cross at (3, 2).

Rule: A solution is a point on both lines at once. It is the crossing.

Each line is drawn from its own equation. The crossing shows only when both lines are on the same grid.

In the table, level means both sides are equal.

The crossing point, checked against both claims
EquationAt (3, 2)Claim saysLevel?
2x + 3y = 122·3 + 3·2 = 1212yes
x − y = 13 − 2 = 11yes

A line's lean is how steeply it slopes up or down. Two lines that lean differently share exactly one point. Line 1 falls 2 for every 3 steps right. Line 2 rises 1 for every 1 step right. Different leans mean one crossing.

A point read between grid marks is only an estimate. Algebra finds the exact pair.

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This track

  1. 0 Start here
  2. 1 One claim with two letters
  3. 2 Checking a pair twice
  4. 3 All the pairs make a line
  5. 4 Two lines and one shared spot
  6. 5 The three things two lines can do
  7. 6 Checkpoint: claims, pairs and lines
  8. 7 The substitution walk
  9. 8 Scale the equations, then take one away
  10. 9 Both roads, one answer
  11. 10 What falls out when nothing is left
  12. 11 Checkpoint: the two algebra roads
  13. 12 The big picture
  14. 13 Track quiz

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