Question

Find the circumference and the area Of the circle with diameter 4yd

Answer 1

Answer:

• circumference: 12.56 yd
• area: 12.56 yd²

Step-by-step explanation:

The formula for circumference is ...

  C = πd

  C = (3.14)(4 yd) = 12.56 yd . . . . . . . . fill in the numbers; do the arithmetic

The circumference is 12.56 yd.

__

Since the diameter is 4 yd, the radius is half that, or 2 yd. The formula for the area is ...

  A = πr²

Fill in the numbers and do the arithmetic.

  A = (3.14)(2 yd)² = 12.56 yd²

The area is 12.56 yd².

_____

Comment on units

In problems such as these, I find it is often useful to keep the units with the numbers. The units can be treated like any variable: multiplied, divided, measures combined by addition or subtraction of "like units".

Just as (2a)² = 2²·a² = 4a², so does (2 yd)² = 2²·yd² = 4 yd². You can be sure that if the units of the problem don't make sense, there is an error somewhere.