To examine the conditions under which the approximations of H3q. (9.23) are valid:(a) Appl...

To examine the conditions under which the approximations of H3q. (9.23) are valid:

(a) Apply the law of cosines to triangle S1S2P in Fig. 9.8c to get

(b) Expand this in a Maclaurin series yielding

(c) In light of Eq. (9.17), show that if (r1, - r2) is to equal a sin θ, it is required that r1, >> a2/λ.