The Cone: Slant First
Part of the Surface Area & Volume section of Coddy's Geometry journey. Lesson 46 of 62.
A cone given by its radius and its height needs one more step before its surface area: the slant height, from the right triangle inside.
This cone has radius 5 and height 12, so s^2 = 5^2 + 12^2 = 169 and s = 13. Then pi × 5^2 + pi × 5 × 13 = 25×pi + 65×pi = 90×pi.
Two steps on the board: tap the slant height and pick Slant height, then tap the cone and pick Surface area of a cone.
Challenge
The cone's radius and height are labelled. Find its exact surface area, then press Check.
Try it yourself
Find the marked part of the figure
Test yourselfThis lesson includes a short quiz. Start the lesson to answer it and track your progress.
All lessons in Surface Area & Volume
1Solids and Their Parts
Faces, Edges and VerticesPrisms and CylindersPyramids and ConesHeight or Slant Height?Spheres and HemispheresRecap: Parts of Solids4Pyramids
Volume of a PyramidThe Slant HeightHeight From the SlantHeight From the VolumeRecap: Pyramids2Volume of Prisms
Volume of a CuboidVolume of a PrismAny Triangle EndA Missing EdgeRecap: Prism Volume3Cylinders
Volume of a CylinderHeight From the VolumeRadius From the VolumeEnough to Find It?Recap: Cylinders6Spheres and Hemispheres
Volume of a SphereHalf a SphereRadius From the VolumeSphere in a CylinderRecap: Spheres9Pyramids and Cones Outside
Surface of a PyramidSlant Height FirstSurface of a ConeThe Cone: Slant FirstRecap: Pyramid Surfaces