**(a)** Consider the addition of rational numbers with same denominators: p/q and r/q

A is called the arithmetic mean of the numbers a and b if and only if a, A, b are in AP.

]]>Triangle Law of Addition of vectors states that, if two vectors are represented in magnitude and direction by the two sides of a triangle taken in the same order, then their sum is represented by the third side taken in the reverse order.

]]>A vector whose initial and terminal points are coincident is called a zero or null or a void vector. The zero vector is denoted by .

]]>**a/sinA = b/sin B = c/sinC = 2R**

**θ = nπ + (−1) ^{n}α**, where n ∈ Z

Divide each term by √(a^{2} + b^{2})

The general solution of sin θ = 0 is given by

**θ = nπ**, n ∈ Z where Z is the set of all integers.