7.9.B
The Standard
determine the circumference and area of circles
Texas Essential Knowledge and Skills for Mathematics
Teacher's field guide
What This Standard Means
What Students Need to Do
- Students use a circle’s radius or diameter to find the distance around it and the space inside it. They work with π and label answers with correct units.
What Mastery Looks Like
- Students correctly identify the radius or diameter from a diagram. They select the right formula, calculate accurately with π, and use linear units or square units as needed.
Common Misconceptions
- Students may use the diameter as the radius or forget to divide it by 2. They may mix up the formulas, square the wrong value, or label area with linear units.
How to Assess It
- Give students a circle with a diameter of 14 centimeters. Ask them to use π = 22/7 to find both measurements and label each answer with correct units.
Lesson moves
Ways to Teach It
Measure round lids with string and rulers, then compare the measured circumference with π times the diameter and calculate each lid’s area.
Ask students to explain why doubling the radius affects circumference and area differently, using formulas or a labeled sketch.
Run a card sort matching circle diagrams, given dimensions, formulas, and calculated answers.
Find the border length and planting area of a circular garden with a diameter of 8 meters.
Keep exploring
Related Standards
- 5.4.H
represent and solve problems related to perimeter and/or area and related to volume
- 7.8.C
use models to determine the approximate formulas for the circumference and area of a circle and connect the models to the actual formulas
- 7.9.C
determine the area of composite figures containing combinations of rectangles, squares, parallelograms, trapezoids, triangles, semicircles, and quarter circles
- 7.5.B
describe π as the ratio of the circumference of a circle to its diameter
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