10r² + 3 = 813
10r² = 813 - 3
10r² = 810
r² = 810 ÷ 10
r² = 81
r = √81
r = <u>9</u>
So, the value of <em>r </em>is 9
<em>Hope </em><em>it </em><em>helpful </em><em>and </em><em>useful </em><em>:</em><em>)</em>
Tetrahedron has 4 faces so it's a pyramid, dodecahedron is 12 faces, octahedron is 8 faces, icosahedron has 20 faces. Easiest way I know to classify them
