12.2 Surface Area of Prisms & Cylinders
Definitions Prism – polyhedron with 2 faces (called bases) that lie in planes. Named by the shape of the bases. Lateral Faces – the faces that are NOT bases (all are ’ogram shaped) Lateral Edges – edges of the lateral faces that are NOT edges of the bases as well. Height (altitude) - distance between the bases. Right Prism – lateral edges are to bases. Oblique Prism – lateral edges are NOT to the bases. (looks slanted)
Right Oblique Triangular Prisms Bases (2 Δs) Lateral faces (3 ll’ograms) height Lateral edges (3) Triangular Prisms
3-D Areas Lateral Area (LA) – the sum of the areas of the lateral faces only. Does not include the area of the bases. Surface Area (S) – the sum of the areas of ALL the faces. Lateral area + area of the bases
Net Defn. – a 2-dimensional representation of a solid. Just think “unfold” the figure and lay it flat. Ex:
To find surface or lateral areas, you could find the areas of each individual face and then add them all together; OR you could use formulas! Thm 12.2 – SA of a rt. Prism S = 2B + Ph B = area of base, P = perimeter of base, h = height of prism What about Lateral Area? * remember: LA is everything BUT the bases! So, LA = Ph
Ex: Find the lateral & surface areas of the triangular prism. LA = Ph P = 6*3 = 18 LA = 18*10 LA = 180 in2 S = 2B + Ph S = 2(15.59) + 180 S = 31.18 + 180 S = 211.18 in2 6 in. 60o 10 in.
Cylinder Defn. – solid with , circular bases. Can be oblique or right. Lateral Area – the area of the curved surface. What does the curved surface look like if laid out flat? Think of the label of a soup can! It’s a rectangle! (area of rectangle = bh) Surface Area – lateral area + area of bases. h h
Let’s look at lateral area 1st! Thm 12.3: SA of a rt. cylinder Let’s look at lateral area 1st! LA = Ch or LA = 2rh So, S = 2B + Ch S = 2r2 + 2rh
Ex: Find the lateral & surface areas of the cylinder. LA = 2rh LA = 2(4)(8) LA = 64 m2 Or 201.06 m2 S = 2r2 + 2rh S = 2(42) + 64 S = 32 + 64 S = 96 m2 Or 301.59 m2 4 m. 8 m.