Surface Area of Prisms & Cylinders Objectives: 1) To find the surface area of a prism. 2) To find the surface area of a cylinder.
Surface Area of a Prism Sa = 2B + Ph Sa = 2*50 + 30*12 Sa = 460 sq m B = area of the base P = perimeter of the base h = height of the prism Calculate: area of the base … B = 5 * 10 = 50 perimeter of the base … P = 2(10) + 2 (5) = 30 height of the prism … h = 12 Sa = 2*50 + 30*12 Substitute: Sa = 460 sq m
Right Prisms vs Oblique Prisms Right Prism – Edges are Altitudes.
Lateral Area – The sum of the areas of the lateral faces (sides) Right Prisms - Lateral Faces are Rectangles A = l•w Base Area – The sum of the areas of the 2 bases Rectangle: A = l•w Triangle: A = ½bh Polygon: A = ½ap Total Surface Area = Lateral Area + Base Area
Ex.1: Use the net to find the Surface Area of the rectangular Prism. Area of Bases: A = l•w 2 different Lats: A = l•w 4 5cm 12 3 3 4 3 5 15 20 15 20 3cm 4cm SA = LA + BA = 70cm2 + 24cm2 = 94cm2 3 12
Ex.2: Find the total surface area of the following triangular prism. 5cm LA = l•w (5 x 12) = 60cm2 (6 x 12) = 72cm2 5cm 12cm 6cm 192cm2 BA = ½bh = ½(6)(4) = 12cm2 x 2 24cm2 5 h SA = LA + BA = 192cm2 + 24cm2 = 216cm2 a2 + b2 = c2 h2 + 32 = 52 h = 4 3 6
Ex.2: Find the total surface area of the following regular hexagonal prism. LA = l•w (10 x 12) = 120m2 x 6 12m 720m2 10 BA = ½ap = ½(8.7)(60) = 260m2 x 2 520m2 10m 30° a SA = LA + BA = 720m2 + 520m2 = 1240m2 5 Tan 30 = 5/a .577 = 5/a a = 8.7
II. Finding Surface Area of a Cylinder Has 2 , // bases Base → Circle C = 2πr A = πr2 r height r h r
Net of a Cylinder: LA is just a Rectangle! LA = 2rh BA = r2 Area of a circle LA = 2rh BA = r2 r Circumference of the circle SA = LA + 2BA
Ex.4: SA of a right cylinder LA = 2rh = 2(6)(9) = 108ft2 = 339.3ft2 6ft Area of Base BA = r2 = (6)2 = 36ft2 9ft x 2 SA = LA + BA = 339.3ft2 + 226.2ft2 = 565.5ft2 = 72ft2 = 226.2 ft2
What did I learn today?? Find the area of the Lats first!! Usually rectangles Be careful, the rectangles are not always the same size. Second, find the area of the Base Rectangle, Triangle, Polygon, or a Circle There are always 2 bases in prisms. Multiply by 2!