# Formulas (Understanding & Application) Formulas are very important. They make solving of problems easier and faster.Its  very important to understand the formula and to apply them at correct place.For example, let us take simple expansion formula(expansion of square of a binomial expression) i.e.  (a+b)2. We know the formula is :-  (a+b)2 = a2 + 2.a.b + b2 . Now in order To apply the formula, We must know that the letters/alphabets ‘a’ and ‘b’ represent the two terms of the binomial expression and understand the formula like this  à the square of a binomial(containing two terms) expression  = square of first + 2 times the product of the two terms + square of the second term.  Let us apply this formula                        Eg. 1: Let us find the square of a binomial expression 3ax+4xy      (3ax+4xy)2 = (3ax)2+2.(3ax).(4xy)+(4xy)2= 9a2x2+24ax2y+ 16y2        Hence,  (3ax+ 4xy)2 = 9a2x2+ 24ax2y+ 16y2 ← Answer    Eg2.  (a+b+c)2   [ Square of a trinomial(containing 3                                     terms) expression ]                           Let us take 1st term as  (a+b)   and   2nd term as  c                     (a+b+c)2=(a+b)2+2(a+b).c+ c2= a2+2.a.b+b2+2a.c+2b.c+ c2                     = a2+b2+c2+2ab+abc+2ac                                 Hence,(a+b+c)2 =  a2+b2+c2+2ab+abc+2ac  ← Answer 