INTEGRATION BY DECOMPOSITION METHOD EXAMPLES

Integrate the following functions with respect to x :

Example 1 :

cos2x/(sin2x cos2x)

Solution :

= ∫[cos2x/(sin2x cos2x)]dx

∫[(cos2x - sin2x)/(sin2x cos2x)]dx

∫[cos2x/(sin2x cos2x)]dx - ∫[sin2x/(sin2x cos2x)]dx

∫(1/sin2x)dx - ∫(1/cos2x)dx

∫cosec2xdx - ∫sec2xdx

= -cotx - tanx + c

Example 2 :

(3 + 4cosx)/sin2x

Solution :

= ∫[(3 + 4 cosx)/sin2x]dx

  = 3∫(1/sin2x)dx + 4∫(cos x/sin2x)dx

= 3∫cosec2xdx + 4cotxcosecxdx

= 3(-cotx) + 4(-cosecx) + c

= -3cotx - 4cosecx + c

Example 3 :


sin2x/(1 + cosx)

Solution :

= ∫[sin2x/(1 + cosx)]dx

∫[(1 - cos2x)/(1 + cosx)]dx

∫[(1 + cosx)(1 - cosx)/(1 + cosx)]dx

∫(1 - cosx)dx

= x - sinx + c

Example 4 :

sin4x/sinx

Solution :

= ∫[sin4x/sinx]dx

= ∫[sin2(2x)/sinx]dx

∫[2sin(2x)cos(2x)/sinx]dx

∫[⋅ 2sinxcosx ⋅ cos(2x)/sinx]dx

∫[⋅ 2cosx ⋅ cos(2x)]dx

2[cos(x + 2x) + cos(-x)]dx

= 2[cos3x + cosx]dx

= 2[(sin3x)/3 + (sinx)] + c

Example 5 :

cos3xcos2x

Solution :

= ∫[cos3xcos2x]dx

= ∫(2/2)[cos3xcos2x]dx

= (1/2)∫(2cos3xcos2x)dx

= (1/2)∫[(cos(3x + 2x) + cos(3x - 2x)]dx

= (1/2)∫[cos5x + cosx]dx

= (1/2)[(sin5x)/5 + sinx] + c

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