If a, b, c, d are in continued proportion, prove that : (i) (ii) (a<sup>2</sup> - b<sup>2</sup>)(c<sup>2</sup> - d<sup>2</sup>) = (b<sup>2</sup> - c<sup>2</sup>)<sup>2</sup> (iii) (a + d)(b + c) - (a + c)(b + d) = (b - c)<sup>2</sup> (iv) a : d = triplicate ratio of (a - b) : (b - c) (v)