There are a number of formulae that need to be known for calculating circle-based shapes.
The surface area of the curved part of a #cone# is `A = pi xx text(base radius) xx text(slant length) = πrl`
P320_z1;P320_z1.png;surface area of a cone
The surface area of a #sphere# is `A = frac(4)(3) xx *π* xx text(radius)^2 = frac(4)(3)πr^2`
P320_z2;P320_z2.png;surface area of a sphere
| 1 | A solid wooden cone has a base diameter of 24cm and a slant length of 40cm. What is the total surface area of the cone? |
| Answer: | 1594.2 cm2 |
Area of curved part = `πrl = π xx (24 ÷ 2) x 40 = 1507.2 text(cm)^2` Area of base = `πr^2 = π xx (24 ÷ 2)^2 = 452.2text(cm)^2` Total area = 1507.2 + 452.2 = 1959.4 cm2 |
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| 2 | A globe has a diameter of 30 cm. What is the surface area of the globe? |
| Answer: | 2826 cm2 |
Area of a globe = `4πr^2` `= 4 xx π xx (30 ÷ 2)^2` = 2826 cm2 |