Update index.html

Typo fix

Author: Gmac4247

index.html

@@ -739,7 +739,7 @@ <h3 style="margin:7px">Circumference of a Circle</h3>
 <h3 style="margin:7px">Volume of a Sphere</h3>
 <br>
 <figure class="imgbox">
-    <img class="center-fit" src="sphere.jpeg" alt="Sphere and isovolumetric cube comparison">
+    <img class="center-fit" src="sphere.jpeg" alt="Sphere and isovolumic cube comparison">
     </figure>
 <br>
 <p style="margin:12px"><strong>The volume of a sphere is defined by comparing it to a cube, since that is the base of volume calculation.</strong></p>