Petty area calculation error fix (#21970)

(window.innerWidth/2) * (window.innerWidth / 2) = ( (window.innerWidth) * (window.innerWidth) )  / 4.    // quarter size

docs/manual/en/introduction/Creating-a-scene.html

@@ -61,7 +61,7 @@
 
 		<p>Next up is the renderer. This is where the magic happens. In addition to the WebGLRenderer we use here, three.js comes with a few others, often used as fallbacks for users with older browsers or for those who don't have WebGL support for some reason.</p>
 
-		<p>In addition to creating the renderer instance, we also need to set the size at which we want it to render our app. It's a good idea to use the width and height of the area we want to fill with our app - in this case, the width and height of the browser window. For performance intensive apps, you can also give <strong>setSize</strong> smaller values, like <strong>window.innerWidth/2</strong> and <strong>window.innerHeight/2</strong>, which will make the app render at half size.</p>
+		<p>In addition to creating the renderer instance, we also need to set the size at which we want it to render our app. It's a good idea to use the width and height of the area we want to fill with our app - in this case, the width and height of the browser window. For performance intensive apps, you can also give <strong>setSize</strong> smaller values, like <strong>window.innerWidth/2</strong> and <strong>window.innerHeight/2</strong>, which will make the app render at quarter size.</p>
 
 		<p>If you wish to keep the size of your app but render it at a lower resolution, you can do so by calling <strong>setSize</strong> with false as <strong>updateStyle</strong> (the third argument). For example, <strong>setSize(window.innerWidth/2, window.innerHeight/2, false)</strong> will render your app at half resolution, given that your &lt;canvas&gt; has 100% width and height.</p>