Update index.html

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Author: Gmac4247

index.html

@@ -3307,7 +3307,7 @@ <h3 style="font-size:160%;margin:7px">
 <p style="margin:12px;">The volume of a sphere is defined by comparing it to a cube, since that is the base of volume calculation.
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-The volume of a sphere equals the cubic value of the square root of its cross sectional area, just like a cube.
+The volume of a sphere equals the cubic value of the square root of its cross-sectional area, just like a cube.
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