Question 9 Solve the given differential equation by variation of parameters. y" + y = sec x Hint: Use the following formula Y = - yu + y,uz = -y1 dx + 2.J dx P W W O y (x) = c 1 cos x + C 2 sin x + cos x In |cos x| + x sin x O y (x) = c 1 cos x + C 2 sin x + cot x In |cos x| + x tan x O y (x) = c 1 cos x + c 2 sin x + sin x In |cos x| + x Cos x O y (x) = c 1 cos x + C 2 sin x + tan x In |cos x| + x cot x