Using Induction: Let n E N. Prove that if f(x) = x^n, then f^(n)(x) = n!. In other words, prove the Formula (d/dx)^n x^n = n! for all n E N. Solution put n=1 (d/dx)^1*x^1 =1! dx/dx=1 1=1 It is true for n=1 let n=k assume that it works thus,(d/dx)^k (x)^k =k! suppose n=k+1 (d/dx)(k+1) (x)^(k+1) =>d/dx)^k d/dx (x)^(k+1) =(d/dx)^k *(k+1) x^(k+1-1) =>(k+1)(d/dx)^k *x^k but (d/dx)^k *x^k =k! substitue (k+1)k! (k+1)! thus it is true for n=k+1 Therefore by principle of mathematical induction it is true for all x.