Polygons
In this course, we will learn the names of polygons with 5 to 10 sides and how to identify them by their number of sides. We will also study the key polygon formulas, including the sum of interior angles and the formula for each interior angle of a regular polygon.
Related Lessons:
Rounding Off By Decimal Places
When rounding by decimal numbers, observe the following key rules:
- All non-zero digits are significant.
- Zeros between non-zero digits are significant.
- If the next digit is 5 or more, round up; if it is less than 5, keep the digit the same.
- 65.456 = 65.46 (2 d.p.)
- 65.451 = 65.45 (2 d.p.)
- Trailing zeros may be significant
- 2.4950 = 2.50 (2 d.p. – note that the ending zero is significant)
Rounding Off By Significant Figures
When rounding by significant figures, observe the following key rules:
- All non-zero digits are significant.
Zeros between non-zero digits are significant. - If the next digit is 5 or more, round up; if it is less than 5, keep the digit the same.
- 8436 = 8000 (1 s.f.)
- 8436 = 8400 (2 s.f)
- 8436 = 8440 (3 s.f.)
- All leading zeros are not significant
- 0.000312 = 0.00031 (2 s.f. by counting the first non-zero from the left)
- Trailing zeros may be significant (i.e. counted)
- 2.4695 = 2.470 (4 s.f. – note that the last zero is significant)
Rounding Exceptions: How to Handle Special Cases
What happens when we need to round a special number such as 9.9995 to 3 decimal places or 3 significant figures?
In this case, the digit being rounded causes a carry-over across several digits. Since the next digit is 5, we round up. Adding 1 to the last retained digit changes 9.999 into 10.000, increasing the value of the number. So we may need to reduce the value of the number.
Hence, the rounded results are:
- 10.000 (3 d.p.)
- 10.0 (3 s.f.).
Similarly, if the number is rounded to 2 decimal places or significant figures, the answers are:
- 10.00 (2d.p.)
- 10 (2s.f.)