SOLUTION: if α and β are zeroes of 3x^2+8x+2 ,find value of α^2+ß^2 1) a^3+ß^3 2) a^4+ß^4 3) α^2+ß^2

Algebra ->  Polynomials-and-rational-expressions -> SOLUTION: if α and β are zeroes of 3x^2+8x+2 ,find value of α^2+ß^2 1) a^3+ß^3 2) a^4+ß^4 3) α^2+ß^2      Log On


   



Question 319305: if α and β are zeroes of 3x^2+8x+2 ,find value of α^2+ß^2
1) a^3+ß^3
2) a^4+ß^4
3) α^2+ß^2

Answer by Edwin McCravy(20063) About Me  (Show Source):
You can put this solution on YOUR website!

The zeros alpha and beta of

3x%5E2%2B8x%2B2 

are also the zeros of

x%5E2%22%2B%228%2F3x%22%2B%222%2F3

which is the original divided through by 3, the coefficient of x%5E2.
Known facts about the relationships between the coefficients and the 
zeros of a monic polynomial tell us that:

-%28alpha+%2B+beta%29+=+8%2F3

and

alpha%2Abeta+=+2%2F3

Since:

-%28alpha+%2B+beta%29+=+8%2F3

then multiplying both sides by -1:

alpha+%2B+beta+=+-8%2F3

Squaring both sides:

%28alpha+%2B+beta%29%5E2+=+%28-8%2F3%29%5E2

alpha%5E2+%2B+2alpha%2Abeta+%2B+beta%5E2+=+64%2F9

and now since alpha%2Abeta+=+2%2F3, we substitute 2%2F3 for alpha%2Abeta:

alpha%5E2+%2B+2%282%2F3%29+%2B+beta%5E2+=+64%2F9

alpha%5E2+%2B+4%2F3+%2B+beta%5E2+=+64%2F9

So 

alpha%5E2+%2B+beta%5E2+=+64%2F9+-+4%2F3+=+64%2F9-12%2F9

alpha%5E2+%2B+beta%5E2+=+52%2F9

--------------------------

1) alpha%5E3%2Bbeta%5E3

We can find that by factoring the sum of two cubes.  We already
have values for alpha%5E2%2Bbeta%5E2 and alpha%2Abeta.



----------------------------

2) alpha%5E4%2Bbeta%5E4

We have 

alpha%5E2%2Bbeta%5E2=52%2F9

Squaring both sides gives:

alpha%5E4+%2B+2alpha%5E2beta%5E2+%2B+beta%5E4+=+2704%2F81

alpha%5E4+%2B+2%28alpha%2Abeta%29%5E2+%2B+beta%5E4+=+2704%2F81

And since alpha%2Abeta+=+2%2F3,

alpha%5E4+%2B+2%282%2F3%29%5E2+%2B+beta%5E4+=+2704%2F81

alpha%5E4+%2B+2%284%2F9%29+%2B+beta%5E4+=+2704%2F81

alpha%5E4+%2B+8%2F9+%2B+beta%5E4+=+2704%2F81

alpha%5E4+%2B+beta%5E4+=+2704%2F81+-+8%2F9

alpha%5E4+%2B+beta%5E4+=+2704%2F81-+72%2F9

alpha%5E4+%2B+beta%5E4+=+2632%2F81

------------------

You stop there but we could show that 

alpha%5E5+%2B+beta%5E5+=+-18848%2F243

and 

alpha%5E6+%2B+beta%5E6+=+134992%2F729

and

alpha%5E7+%2B+beta%5E7+=+-966848%2F2187

and

alpha%5E8+%2B+beta%5E8+=+6924832%2F6561

and as far as we like.

Edwin