Precalculus
posted by Emily .
Solve the equation x^3  2x + 4 = 0.
==> I know the answer is 2, but I can't seem to remember how to solve these by hand without using a graphing calculator. Any help is greatly appreciated!! :)

Precalculus 
Reiny
Unless they factor, cubic equations cannot be easily solved "by hand"
In this case, try subbing ±1 and ±2 into the equation to get a zero.
You were right to find that x = 2 works
so (x+2) must be a factor.
Use long algebraic division or synthetic division to find the other factor to be (x^2  2x + 2)
using the quadratic formula on
x^2  2x + 2 = 0 gives me two complex roots, namely (1 ± i)/2 
correction  Precalculus 
Reiny
the two complex roots should have been just
1 ± i 
Precalculus 
Emily
Ohhh I see. Thanks Reiny this helped a lot!! :)
Respond to this Question
Similar Questions

solving an exponential equation
Count iblis helped me solve this in another thread. But I am looking for an easier method. Can anyone help? 
math
solve for x without using a calculator 5^(x+1) = 25 i know that x would equal 1 because 5^2 is 25, but i don't know how to show how to solve it All you need to do is what you just did: Explain that if x = 1, the equation is satisfied. … 
Algebra 2
I need help with this problem because I do not have a graphing calculator. Explain how you would solve this equation using your graphing calculator in five steps then give the solution. 2x 3y=8 5x+ 4y= 11 Also how do you determine … 
Algebra 2
I need help with this problem because I do not have a graphing calculator. Explain how you would solve this equation using your graphing calculator in five steps then give the solution. 2x 3y=8 5x+ 4y= 11 
Algebra2/Trig
Find all the zeros of the function and write the polynomial as a product of linear factors. g(x)=3x^34x^2+8x+8 On my graphing calculator it says that it is 2/3. But when I do it by hand using synthetic division, I don't get a zero. … 
algebra
I just need a quick check before I hand in my work if you would...Thanks. 1. I am to use the intercepts to graph the equation x+3y=6 I used the formula y=mx+b using 3 and 6 for x I got these as my ordered pairs to graph (3, 1), (6, … 
ConfusedMath
Your calculator gives an answer of x=1.1578074156, y=2E13 when using ROOT or ZERO in the graphing mode. Give the coordinates of the xintercept your calculator has given you to the nearest thousandth. <<< ? 
statistics/calculus
e^(10)e^(10x)x/(e^(10)11)=0.25 and e^(10)e^(10x)x/(e^(10)11)=0.75 Solve both for x. Can you solve both of these for x without a Ti89 calculator? 
Algebra II Part 2
Use a graphing calculator to solve the equation 3 cos t=1 in the interval from 0 to 2 p.Round your answer to the nearest hundredth 
precalculus
Solve the system of equations at the right by the method of substitution. Verify your results by using a graphing utility. x2+y24x+6y5=0, x+y+5=0 answer: x=y5 (y5)2+y24(y5)2+6y5=0 y=√55, y=5√5 x+√55+5=0 x=√5 …