Answer the following questions about fundamental trigonometric identities.
a. (i) Starting with sin2θ+cos2θ=1, derive the relation sec2θ−tan2θ=1.
b. (ii) Using a similar method, derive csc2θ−cot2θ=1 from the primary identity.
c. (iii) Explain, in words and symbols, why the expressions sec2θ−tan2θ and csc2θ−cot2θ are each equal to a constant for every permissible value of θ.