Develop, verify, and apply rules or expressions for the area of rectangles. Area and Perimeter(Quadrilaterals and Circles): Grade 8 Lesson 32.03. Estimate and determine the surface area of a right rectangular prism, without using a formula.
http://staff.argyll.epsb.ca/jreed/math8/strand3/3206.htm
Area and Perimeter: Quadrilaterals and Circles: Grade 8 Lesson 22.03. Use the Pythagorean relationship to calculate the measure of the third side of a right triangle, given the other two sides.
http://staff.argyll.epsb.ca/jreed/math8/strand3/3206.htm
The area of a regular polygon is half its perimeter multiplied by the distance from its center to its sides, and the corresponding formula (that the area is half the perimeter times the radius, i.e. 1⁄2 × 2πr × r) holds in the limit for a circle.
https://en.wikipedia.org/wiki/Area_of_a_disk
The area of a regular polygon is half its perimeter times the apothem. As the number of sides of the regular polygon increases, the polygon tends to a circle, and the apothem tends to the radius. This suggests that the area of a disk is half the circumference of its bounding circle times the radius.
https://en.wikipedia.org/wiki/Area_of_a_disk
Also, let each side of the polygon have length s; then the sum of the sides, ns, is less than the circle circumference. The polygon area consists of n equal triangles with height h and base s, thus equals 1⁄2nhs. But since h < r and ns < c, the polygon area must be less than the triangle area, 1⁄2cr, a contradiction.
https://en.wikipedia.org/wiki/Area_of_a_disk
Key Terms: area, surface area, volume, right prism, triangular prism, rectangular prism, cube, cylinder, face, congruent, equilateral, net, prism. Prerequisite Skills: Describe patterns and generalize the relationships by determining the areas and perimeters of quadrilaterals, and the areas and circumferences of circles.
http://staff.argyll.epsb.ca/jreed/math8/strand3/3206.htm
In geometry, the area enclosed by a circle of radius r is πr2. Here the Greek letter π represents a constant, approximately equal to 3.14159, which is equal to the ratio of the circumference of any circle to its diameter.
https://en.wikipedia.org/wiki/Area_of_a_disk
The area of a triangular-shaped mat is 18 square feet and the base is 3 feet. Find the height. Solution: In this example, we are given the area of a triangle and one dimension, and we are asked to work backwards to find the other dimension.
http://www.mathgoodies.com/lessons/vol1/area_triangle.html
We will look at several types of triangles in this lesson. To find the area of a triangle, multiply the base by the height, and then divide by 2. The division by 2 comes from the fact that a parallelogram can be divided into 2 triangles. For example, in the diagram to the left, the area of each triangle is equal to one-half the area of the parallelogram. Since the area of a parallelogram is , the area of a triangle must be one-half the area of a parallelogram.
http://www.mathgoodies.com/lessons/vol1/area_triangle.html
estimate, measure, and calculate the surface area and volume of any right prism or cylinder.
http://staff.argyll.epsb.ca/jreed/math8/strand3/3206.htm
how to find the surface area of a triangle
To find the surface area of a triangle, multiply the base by the height, and then divide by 2.  To find the area of a triangle, multiply the base by the height, and then divide by 2. The division by 2 comes from the fact that a parallelogram can be divided into 2 triangles.