Need to Know
Ratio
The rules you must have ready for the exam.
How to use this: say each rule in your head, then tap Show me to check.
Equal intercepts
1 ruleRule 01
Parallel lines
Parallel lines cut transversals in the same ratio. Equal pieces one side → equal pieces the other.
Line parallel to a side
1 ruleRule 02
The two ratios
|AP|/|PB| = |AQ|/|QC|
|AP|/|AB| = |AQ|/|AC| = |PQ|/|BC|
Method
1 ruleRule 03
Solve it
Write the equal fractions with matching parts, then cross-multiply.
Nested triangles
1 ruleRule 04
Similar shapes
A line parallel to the base makes a smaller similar triangle — use the same ratios.
Mathslive.ie · Ratio · Need to Know