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RATIO

Exam Cog
①EQUAL INTERCEPTS

Parallel lines cut transversals in the SAME ratio

|AB|=|BC| → |DE|=|EF|

②LINE PARALLEL TO A SIDE

|AP|/|PB| = |AQ|/|QC|

|AP|/|AB| = |AQ|/|AC| = |PQ|/|BC|

★ Match part-to-part OR part-to-whole (not mixed)
③METHOD
  1. Label the pieces
  2. Write the equal fractions
  3. Cross-multiply
  4. Solve for the unknown
④WHOLE vs PART

|AB| = |AP| + |PB| (the whole side)

Be careful which one the question gives.

⑤NESTED TRIANGLES

A parallel line makes a smaller similar triangle

x/12 = 3/8 → 8x = 36

⑥WATCH-OUTS
⚠ Don’t mix part-to-part with part-to-whole in the same fraction.