Help Polynomials Question (1 Viewer)

[kevinsta]

Given two roots of 2x^3 -kx^2+8=0 are equal, find k.

Need help on this question so hard.

 

[Kurosaki]

Given two roots of 2x^3 -kx^2+8=0 are equal, find k.

Need help on this question so hard.

Let the roots be alpha, alpha and beta.
Using sum of roots, then
Using product of roots,
Using sum of roots two at a time, then
We can rearrange that last one to be: , from which follows:
We can substitute that into the product of roots, giving us .
From here, solve for alpha, then beta, and hence deduce k by sum of roots.