Vol. 2 · Balances and graphs

Equations and Systems of Equations

A companion to 《方程与方程组》 by Ge Jun · 18 stops ·

Vol. 1Vol. 2Vol. 3Vol. 4Vol. 5Vol. 6Vol. 7Vol. 8

  1. Ch. 1Look at a and 1A letter is a slot: always true means identity; true for a few means equation.ConceptM22
  2. Ch. 2Linear Equations in One UnknownAn equation is a level balance. Do the same to both sides until x is revealed.Skill
  3. Ch. 3Linear Equations with Letter CoefficientsAt ax = b, do not divide yet: a ≠ 0; a = 0, b ≠ 0; both 0. Three endings.SkillM4M18
  4. Ch. 4Using and Rearranging Linear EquationsAbsolute values, repeating decimals: split into pieces or × 10, and get ax = b.Skill
  5. Ch. 5Linear Systems in Two UnknownsEquations are lines. Elimination draws a vertical line through their crossing.Skill
  6. Ch. 6Linear Systems in Several UnknownsThree unknowns: eliminate one, then another, then walk back down the staircase.Skill
  7. Ch. 7Learning to Complete the SquareFill the corner of x²+bx to get a square; squares are never negative.SkillM1
  8. Ch. 8Solving Quadratic EquationsSquare roots, completing the square, formula, factoring. Pick the easiest road.SkillM1
  9. Ch. 9The DiscriminantWithout solving, Δ = b² − 4ac tells you: two real roots, one, or none.ConceptM3
  10. Ch. 10Vieta's FormulasThe sum and product of the roots sit in the coefficients. Check Δ first.ConceptM3M5
  11. Ch. 11Higher-Degree EquationsSwap a repeated block for t, or factor, to reduce it to a quadratic.SkillM2
  12. Ch. 12Fractional EquationsMultiply by the common denominator, then check every root, since it may be 0.SkillM2
  13. Ch. 13Radical EquationsSquaring removes the root but lets in ghost-branch roots, so always check.SkillM2
  14. Ch. 14Quadratic Systems in Two UnknownsSolutions are common points. Substitute a linear equation, or use Vieta.SkillM2M5
  15. Ch. 15Integer Solutions of EquationsInteger solutions are lattice points: divide, factor, bound, check parity.MethodM6M12M15
  16. Ch. 16Integer Roots of Quadratic EquationsFor integer roots Δ must be a perfect square; Vieta and factoring do the rest.MethodM3M4M13
  17. Ch. 17Word Problems with EquationsDraw the story as a distance–time graph. Where the lines cross is the solution.Skill
  18. Ch. 18A Map of EquationsThe whole volume in one picture: every equation reduces to ax = b.Concept