Mathematics Class 9
Linear Equations in Two Variables
An equation that carries two letters, why one solution of a pair is a whole pair of numbers, the two lines a pair draws on one plane, the three things two lines can do, the read-off that is only an estimate, and the two algebra routes — substitution and elimination — that always land on the same answer or agree that there is none.
14 lessons · ~92 min total
Track progress — 0 of 14 lessons read 0%
Lessons in this topic
- 0 Start here A roadmap: two letters in one equation, checking a pair, lines, and the two methods that agree. · 4 min You are here
- 1 One claim with two letters Two letters in one claim, each with power 1. A solution is a pair. · 6 min
- 2 Checking a pair twice A pair is a solution only if both equations come out level. · 6 min
- 3 All the pairs make a line Every pair of one equation lies on one line, and every point of the line fits. · 7 min
- 4 Two lines and one shared spot A solution is the point where the two lines cross. · 7 min
- 5 The three things two lines can do Two lines cross once, never, or lie on one line: one, none or all solutions. · 7 min
- 6 Checkpoint: claims, pairs and lines A graded check on the first five ideas — what a solution is, checking twice, points of one line, the read-off and the estimate, and the three verdicts. · 6 min
- 7 The substitution walk Name one letter, put its name in the other equation, then walk back. · 7 min
- 8 Scale the equations, then take one away Scale a whole equation so one letter matches, then subtract. That letter falls out. · 7 min
- 9 Both roads, one answer Substitution and elimination reach the same crossing. Run both on one pair. · 7 min
- 10 What falls out when nothing is left What elimination leaves gives the verdict: a number, a false claim, or 0 = 0. · 7 min
- 11 Checkpoint: the two algebra roads A graded check on substitution, elimination, the agreement of the two roads, and the verdict hiding in the fall-out. · 6 min
- 12 The big picture Nine ideas, one crossing, and the three things two lines can do. · 6 min
- 13 Track quiz A cheat-sheet table and nine questions on its ideas. · 9 min
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