Algebraic Identities and Factorisation

• (x + a) (x + b)= x² + (a + b) x + ab

Example:

Find 206 × 198.

Solution:

We have,

206 × 198 = (200 + 6) (200 – 2)

   = (200)² + (6 + (– 2)) × 200 + (6) (– 2)               [Using identity (x + a) (x + b)= x² + (a + b) x + ab]

   = 40000 + 800 – 12

    = 40800 – 12

   = 40788  

• An identity is an equality which is true for all values of the variables in it. It helps us in shortening our calculations.
•  Identities for "Square of Sum or Difference of Two T…