Question 913338
r*t=d
7/(r-4)+7/(r+4)=8/1
Multiply thru by 1*(r-4)(r+4)
7*1(r+4)+7*1(r-4)=8(r^2-16)
7r+28+7r-28=8r^2-128
r^2-14r-128=0
r=12.2321245982865

*[invoke complete_square "r", 2, -14, -128]
*[invoke quadratic "r", 2, -14, -128]