Linear Inequalities — Digital SAT SAT Math revision notes
A 3-page visual revision sheet for Linear Inequalities, written for Digital SAT SAT Math. Formulas, diagrams and the traps that cost marks, laid out to be read the night before rather than the term before. Free, and it opens inside CapCompass.
Page 1 as PDFA preview of page 1 — all 3 pages open full size in the app.
Linear Inequalities in one look
solve it like an equation, with one rule that can turn the whole thing around
The rules, and the one that bites
adding or subtracting keeps the signa < b ⇒ a + c < b + c
multiplying by a positive keeps ita < b, k > 0 ⇒ ka < kb
multiplying by a negative FLIPS ita < b, k < 0 ⇒ ka > kb
at least k, no less than kx ≥ k
at most k, no more than kx ≤ k
Q. Solve 5 - 3x < 2x + 20.
gather the x terms on the left: 5 - 3x - 2x < 20
5 - 5x < 20, then subtract 5: -5x < 15
divide both sides by -5, and flip the sign because -5 is negative
Answer: x > -3
Four signs, and the words that hide them
greater than: more than, over, exceeds. The boundary is excluded
at least: no less than, minimum of, a floor. The boundary counts
less than: under, below, fewer than. The boundary is excluded
at most: no more than, maximum of, capacity, budget. The boundary counts
Equation vs Inequality
Equation
the answer is a single value of x
the graph of a two-variable one is a line
every legal move keeps the equals sign as it is
Inequality
the answer is a whole range of values
the graph of a two-variable one is a region on one side of a line
dividing by a negative reverses the sign
Page 1 of 3. The full sheet, all 3 pages, opens free in the app.
These notes are not a standalone PDF. CapCompass plans SAT Math chapter by chapter against your real exam dates and free hours, and when the plan reaches Linear Inequalities the sheet opens inside the study block itself — at the page covering the sub-topic that block is on, with the timer still running. Revision arrives at the moment the plan says revise, instead of having to be gone looking for.