Pearson Geometry Common Core, 2011
PG
Pearson Geometry Common Core, 2011 View details
3. Surface Areas of Pyramids and Cones
Continue to next subchapter

Exercise 27 Page 714

Find the lateral area of a cone, the lateral area of a cylinder, and the base area of the cylinder.

About 471 square feet

Practice makes perfect
Let's analyze the given composite solid.
We are asked to find its surface area. It consists of three parts.
  1. The lateral area of a cone with the radius of r= 5 feet and a height of h= 12 feet.
  2. The lateral area of a cylinder with the radius of r= 5 feet and a height of h= 6 feet.
  3. The base area of the cylinder.First, let's use the Pythagorean Theorem for right triangle â–ł ABC to find the slant height of the cone, l.
    BC^2+ AB^2= AC^2
    5^2+ 12^2= l^2
    â–Ľ
    Solve for l
    25+144= l^2
    169= l^2
    l^2=169
    l=sqrt(169)
    l= 13
    Therefore, the slant height of the cone is l= 13 feet. Let's find the areas.
    Figure Cylinder Cone
    Radius r= 5 r= 5
    Height h= 6 h= 12
    Slant Height - l= 13
    Lateral Area L.A.=2Ď€ r h L.A.=Ď€ r l
    L.A.=2Ď€( 5)( 6)=60Ď€ L.A.=Ď€( 5)( 13)=65Ď€
    Base Area B=Ď€ r^2 -
    B=Ď€( 5)^2=25Ď€ -
    The lateral area of the cone is 65Ď€ square feet, the lateral area of the cylinder is 60Ď€ square feet, and the base area of the cylinder is 25Ď€ square feet. Now, let's add them together to find the surface area of the solid, \text{S.A.}_\text{solid}. \begin{aligned} \text{S.A.}_\text{solid}&=\textcolor{darkorange}{65\pi}+\textcolor{darkorange}{60\pi}+\textcolor{darkviolet}{25\pi} \\ &\Downarrow \\ \text{S.A.}_\text{solid}&=150\pi \end{aligned} Finally, we will round the surface area to the nearest whole number.
    \text{S.A.}_\text{solid}=150\pi
    \text{S.A.}_\text{solid}=471.238898\ldots
    \text{S.A.}_\text{solid}\approx 471
    The surface area of the given solid is about 471 square feet.