\(r = {\sqrt{8^2-15^2}}\)

r=sqrt(8^2 - 15^2) Square both sides

r^2 =(8^2 - 15^2)

r^2 =(64 - 225)

r^2=-161 =-1 x 161 Take the sqrt of both sides

r =i sqrt(161)

r =12.688577 i