Expand: e ^x cos x or Prove that e ^x cos x = (1+x-(2x^3)/3!-(2^2 x^4)/4!+⋯)

Higher Engineering Mathematics B.S Grewal Solutions Differential Equations and its Applications Exercise 4.5 Question 12 Expansion of series Expand : e ^x cos x Prove that: e ^x cos x = (1+x-(2x^3)/3!-(2^2 x^4)/4!+⋯)