In reviewing the chapter's "the cost of debt," equation 9-1 shows "bondholder's required rate of return (rb)" in the denominators. What's the different term we used for that rate?

(9-1) interest paid in year 2 Bond market price = + 2 1+ ) rate of return(ro) interest paid in year 1 bondholder's required 1+ rate of return(ru) interest paid in year 3 bondholder's required 1+ rate of return(ro) + + 3 (1+ principal bondholder's required rate of return(r)