Substitution, elimination and cross-multiplication. Then equations that become linear after a change of variable, and word problems about numbers, ages, speeds, money and geometry.
3 lessons, about 1 h 15 min3 simulations10 problems3 practice questionsPython in every lesson
Created by StemPy LabA pair of equations can be solved exactly without drawing it. Substitution writes one letter in terms of the other. Elimination adds or subtracts the equations to remove a letter. Both find the single crossing point of the two lines.
Cross-multiplication solves a pair in one step from its six coefficients. Some pairs are not linear in x and y, but become linear in 1 over x and 1 over y. A change of letters turns them into pairs we can solve.
Many everyday problems have two unknown quantities and two facts about them. Each fact becomes an equation. Solving the pair gives both quantities, and checking against the words of the problem catches mistakes.
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