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To calculate the perimeter of a rectangle, add the lengths of all four of its sides. For the rectangle shown, the side lengths are 2 ft, 6 ft, 2 ft, and 6 ft, giving the expression $P = 2 + 6 + 2 + 6$.

Conditions: Use all side lengths of the shape.; Units must be consistent; here all lengths are in feet.

To calculate the perimeter of a rectangle, add the lengths of all four of its sides. For the rectangle shown, the side lengths are 2 ft, 6 ft, 2 ft, and 6 ft, giving the expression $P = 2 + 6 + 2 + 6$.

Conditions: Use all side lengths of the shape.; Units must be consistent; here all lengths are in feet.

By placing strips of height $2\pi r$ along the radius axis, their tops form a linear graph. As the partition width goes to zero, the step-function approximation converges to the area under the line $y=2\pi x$.

Conditions: Function $f(r) = 2\pi r$ is linear; Partition width $\Delta r \to 0$

By placing strips of height $2\pi r$ along the radius axis, their tops form a linear graph. As the partition width goes to zero, the step-function approximation converges to the area under the line $y=2\pi x$.

Conditions: Function $f(r) = 2\pi r$ is linear; Partition width $\Delta r \to 0$