Tion of light ns equation figure 13.4 and the small-angle approximation imply that de- (equation 13.12, where δ~4gm/尼 4gwb (equation 13.11) and b~ de (from the diagram). the summary claims that together these imply that for the angle θ of images formed by a gravitational lens. exercise 13.6.1. verify that this is true. exercise 13.6.2. the solutions to this equation are θ±-(β± the θ+ solution is clearly outside the einstein ring angle θε. show that meaning that the θ solution is inside the ring. (hint: argue that so, and use this information in equation 13.13, above.) s0, and then