Solve this quadratic(?)

  • Thread starter 1/2"
  • Start date
  • #1
99
0
While solving an problem , i came to this quadratic
x2- 8x +4 =0
I couldn't break up 8x so i to solve it like this,
x= {-(-8)+√(8 2+ 4x1x4)}/2x1,{-(-8)-√(8 2+ 4x1x4)}/2x1
but the answers are coming way too absurd and negative.

The actual problem is:
"A hollow right cylinder of uniform thickness is made from the material obtained by melting a solid sphere of copper.If the diameter of the sphere is 12 cm,the height of the cylinder is 72 cm and the external radius of the base of the cylinder is 4 cm then find the thickness of the cylinder to two decimal places. "
And answer according to the book is 0.54 cm( which i am not getting !)


My doing any mistake in calculating or in the formulas?
Please help .I would be extremely grateful!
 

Answers and Replies

  • #2
360
0
It's just a silly little arithmetic mistake. The quadratic formula is
[tex]
x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}
[/tex]

You have pluses inside the radical in both cases.
 
  • #3
99
0
Yes , i did that .
So whats wrong?
 
  • #4
Borek
Mentor
28,676
3,167
You were already told - you have plus inside the radical. Formula calls for minus.
 
  • #5
360
0
Like I said, you have [tex] \sqrt{b^2 + 4ac} [/tex] instead of [tex] \sqrt{b^2 - 4ac} [/tex].
 

Related Threads on Solve this quadratic(?)

  • Last Post
Replies
10
Views
2K
  • Last Post
Replies
2
Views
1K
Replies
21
Views
3K
Replies
5
Views
1K
  • Last Post
Replies
3
Views
1K
Replies
2
Views
1K
Replies
12
Views
939
  • Last Post
Replies
2
Views
2K
  • Last Post
Replies
2
Views
2K
  • Last Post
Replies
5
Views
1K
Top