The box 13.7 the ratio of image brightness to the source brightness equations 13.16 and 13.15 imply that 14.10.|10, where ao, -(1tre ) 4=bab (13.19) we also have 0,= (bvb + 40, ) from equation 13.14. the claim in equation 13.17 is that the above imply that t-pe. p; 1012) 317) exercise 13.7.1. verify that this is correct. exercise 13.7.2. verify that this ratio is always positive. (hint: argue that for any positive x, x+ (1/x) –220.)