A resistor with resistance R is connected to a battery that has emf 15.0[V] and internal resistance r = 0.38[Ω].
For what two values of R will the power dissipated in the resistor be 78.0 W?
The Attempt at a Solution
At this point I should be able to plug in what I know, and I get roughly
However that is not right, I have tried again making sure I kept my sig figs in order and all that good stuff, I get a couple similar but different answers, still all wrong though.
I have only one attempt left and it's worth 27% of the grade on this HW so any help would be appreciated greatly.
This is an image of my attempts, the problem, and how the solutions manual did the quadratic.