Literal Numbers
We have mentioned earlier that the letters represent the numbers. These letters are called literal numbers and obey all the rules of arithmetic. 
Note :  5 × p × q = 5pq. 5, p and q are factors of 5pq. 5 is a numerical factor and p, q are literal factors.

Power of literal numbers 
We have read earlier that 2 x 2 x 2 = 23 and (–3) x (– 3) = (–3)2      Similarly, a x a x a = a3 and (– y) x (– y) x (– y)  x (– y) = (–y)4 
a3 is read as 'a to the power three' or 'a raised to the power three' or 'a cube' or 'third power of a' and (–y)4 is read as '–y to the power four' or '–y raised to the power four' or fourth power of –y'. 
In a3, a is called base and 3 is called exponent or index. 

Coefficient
The number expressed in figures or symbols, standing before an algebraic term as a multiplier is called its coefficient. Thus in 3abc, 3 is the coefficient of abc, 3a is the coefficient of bc and 3ab is the coefficient of c. 

Ex.1     Write down the coefficient of :
(a) x in 3xy    (b) abc in – 5abc     (c) y in 2xyz   (d) a2 in – a2bc 

Sol.     (a) 3y             (b) – 5            (c) 2xz             (d) – bc 

Ex.2 Write down the numerical coefficient in each of the following :
           (a) 5 ab         (b) – 3xyz      (c) px          (d) –y 
Sol.    (a) 5              (b) –3            (c) 1            (d) – 1 

Ex.3     If a = 2, b = 3, c = 4, find the value of : 
           (a)     3a – b + 2c 
           (b)     a2 – b2 + c2        
           (c)     ab – 3abc – 2ac 

Sol.    (a)     3a – b + 2c = 3 x 2 – 3 + 2 x 4 = 6 – 3 + 8 = 11 
          (b)     a2 – b2 + c2  = 22 – 32 + 42 = 4 – 9 + 16 = 11 
         (c)     ab – 3abc – 2ac = 2 x 3 – 3 x 2 x 3 x 4 – 2 x 2 x 4 = 6 – 72 – 16 = – 82 

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