If the price of a bond can be written as the present value of its coupons and principal where:

P= C * [ [ (1 - 1 / (1 + y)^n ] / y] + [ A / (1+y)^n ]

where C is the semi-annual coupon, A the principal and y is the required yield.

(a) what is the the derivative of this expression with respect to its required yield.
(b) Derive an expression for modified duration.
(c) Hence derive an expression for the convexity measure.

Last two parts are a mathematical-finance based questions. 1st part is standard differentiation.

Can any one help me with any any part of this question??