8th Grade · The Number System
Rational Approximation
8.NS.A.2
Definition
A rational number (fraction or decimal) used to estimate an irrational number. Found by squeezing the value between closer and closer rational bounds.
Teach it
Where it is taught, with guided notes, practice, homework, an exit ticket and an interactive Teacher Deck.
Examples
- √2 is between 1 and 2, then between 1.4 and 1.5, narrowing to about 1.41.
- Square the guess, compare to the target, then narrow the range one decimal place at a time.
Key rule
Squeeze the irrational number between closer and closer rational bounds.
Memory hook
Get closer and closer with decimals.