Quadratics help? Surface area involved
Favorites|Homepage
Subscriptions | sitemap
HOME > Mathematics > Quadratics help? Surface area involved

Quadratics help? Surface area involved

[From: ] [author: ] [Date: 11-05-03] [Hit: ]
Since there are 6 sides to the cube,But a negative length doesnt make sense, even though mathematically x = -8 solves the equation, we reason that this is not a physical answer,......
OK, i know the answer, but i don't know how they got there (or the reasoning). Here's the question: The surface area of a cube is 384 cm^2. Find the length of one edge. I saw this in class, but I didn't follow it very well. All that was on the blackboard said:
6x^2=384
divide both sides by six

x^2=64
√x^2=√64
x=8

Now, I get that if a cube has six faces, and I let one face =x, that I will get 6x. But how do I get 6x^2 out of that? What is the reasoning behind the square symbol?

-
The area of a square of side x is:

x * x = x² (by definition of x²)

Since there are 6 sides to the cube, there are six x²'s:

6x² = 384
--> divideby 6

x² = 64
--> take the square root

x = ±√64 = ±8

x = 8 or -8

But a negative length doesn't make sense, even though mathematically x = -8 solves the equation, we reason that this is not a physical answer, so we just use +8:

x = +8
1
keywords: involved,area,help,Quadratics,Surface,Quadratics help? Surface area involved
New
Hot
© 2008-2010 http://www.science-mathematics.com . Program by zplan cms. Theme by wukong .