Real solutions to a polynomial

Hi, I am stuck to this task: I am trying only to get the real solutions to the function

A = [1 -12 55 -120 124 -80]

B = roots(A)

[Scott MacKenzie]

First of all

A = [1 -12 55 -120 124 -80] 

is not a function. But

A = [1 -12 55 -120 124 -80] 
B = roots(A)

yields

B =
        4.699 +          0i
        3.067 +     1.6505i
        3.067 -     1.6505i
      0.58351 +      1.031i
      0.58351 -      1.031i

so, all the roots for the polynomial with the terms in A are imaginary, except the first:

>> isreal(B(1))
ans =
  logical
   1

[Robert Bag]

I did this: I got "good" answers for a and d but not for the ones in the middle;

A = x^5 - 12*x^4 + 55*x^3 - 120*x^2 + 124*x == 48;

a = solve(A,x,'Real',true)

B = 5*x^6 - x^4 + 70*x^2 - 10*x == 50;

b = solve(B,x,'Real',true)

C = 3*x^5 - x*4 - 12*x^3 + 12*x^2 == 10;

c = solve(C,x,'Real',true)

D = x^5 - 13*x^4 + 64*x^3 - 152*x^2 + 176*x == 80;

d = solve(D,x,'Real',true)

[Robert Bag]

>> Matlab412

a =

1

2

2

3

4

b =

root(z^6 - z^4/5 + 14*z^2 - 2*z - 10, z, 1)

root(z^6 - z^4/5 + 14*z^2 - 2*z - 10, z, 2)

c =

root(z^5 - 4*z^3 + 4*z^2 - (4*z)/3 - 10/3, z, 1)

root(z^5 - 4*z^3 + 4*z^2 - (4*z)/3 - 10/3, z, 4)

root(z^5 - 4*z^3 + 4*z^2 - (4*z)/3 - 10/3, z, 5)

d =

2

2

2

2

5

[Robert Bag]

O know b and c are not monomial and coefficents of highest order is non-zero though

Answer 1

[Walter Roberson]

A = randi([-9 9], 1, 6)

A = 1×6

-7 -4 4 4 -2 9

B = roots(A)

B = 
  -1.0813 + 0.6487i
  -1.0813 - 0.6487i
   1.0967 + 0.0000i
   0.2472 + 0.8223i
   0.2472 - 0.8223i

B(imag(B)==0)

ans = 1.0967