Finding Solutions for y^4+4y-69 - Without Advanced Math Tools

phillyolly
Messages
157
Reaction score
0

Homework Statement



Solving y^4+4y-69, I got the following:
By manually plugging in, I found that y= -3 and y=2.76.

However, I would like to ask you if there are other good, efficient ways to find solutions?
(Without using sophisticated math tools. Imagine, I have this prob on the exam)

Thank you!
 
Physics news on Phys.org
phillyolly said:

Homework Statement



Solving y^4+4y-69
You can't "solve" an expression. You can, however, solve an equation or inequality. Is the equation y^4 + 4y - 69 = 0?
phillyolly said:
, I got the following:
By manually plugging in, I found that y= -3 and y=2.76.

However, I would like to ask you if there are other good, efficient ways to find solutions?
(Without using sophisticated math tools. Imagine, I have this prob on the exam)

Thank you!
I don't know of any ways to solve quartic (fourth-degree) equations analytically, but there might be some. There are ways to solve cubics (third-degree), but even they are fairly involved to solve.

If you don't require exact solutions, there are lots of ways to find approximate solutions, such as Newton's method, and quite a few others.
 
There are two things I don't understand about this problem. First, when finding the nth root of a number, there should in theory be n solutions. However, the formula produces n+1 roots. Here is how. The first root is simply ##\left(r\right)^{\left(\frac{1}{n}\right)}##. Then you multiply this first root by n additional expressions given by the formula, as you go through k=0,1,...n-1. So you end up with n+1 roots, which cannot be correct. Let me illustrate what I mean. For this...
Back
Top