INTEGRATION OF TRIGONOMETRIC FUNCTIONS

Compute each of the following integrals.

Problem 1 :

∫ sin x dx

Solution :

Given, ∫ sin x dx

= -cos x + C 

Problem 2 :

∫ cos 5x dx

Solution :

Given, ∫ cos 5x dx

Let u = 5x, du = 5 dx

dx = 1/5 du

= 15 cos u du= 15 sin u + C= 15 sin 5x + C

Problem 3 :

∫ cos x sin4x dx

Solution :

Given, ∫ cos x sin4x dx

u = sin x, du = cos x dx

= ∫ u4 du

= u5/5 + C

= (1/5) sin5x + C

Problem 4 :

∫ csc2 x dx

Solution :

Given, ∫ csc2 x dx

= -cot x + C 

Problem 5 :

∫ tan x dx

Solution :

Given, tan x dx= sin xcos x dxu = cos xdu = -sin x dxdx = -dusin x= sin xu · -dusin x= -1u du= -In |u| + C=- In|cos x| + C

Problem 6 :

∫ cot x dx

Solution :

Given, cot x dx= cos xsin x dxu = sin xdu = cos x dx= 1u du= In |u| + C= In|sin x| + C

Problem 7 :

∫ sec x dx

Solution :

Given, sec x dx= sec x · sec x + tan xsec x + tan x dx= sec2 x + sec x tan xsec x + tan x dxu = sec x + tan xdu = sec x tan x + sec2x dx= 1u du= In |u| + C= In|sec x + tan x| + C

Problem 8 :

∫ csc x dx

Solution :

Given, csc x dx= csc x · csc x + cot xcsc x + cot x dx= csc2 x + csc x cot xcsc x + cot x dxu = csc x + cot xdu = -csc x cot x + -csc2x dxdx = du-csc x cot x - csc2x=csc2 x + csc x cot xu du-csc x cot x - csc2xcsc2 x + csc x cot xu du-csc x cot x + csc2x= -1u du=- In |u| + C=- In|csc x + cot x| + C

Problem 9 :

sin2 x dx

Solution :

Given, sin2 x dx=1 - cos 2x2 dx=12 1 - cos 2x dx= 12dx - cos 2x dx= 12x - sin 2x2 + C= 12x - 14 sin 2x + C

Problem 10 :

sin3 x dx

Solution :

Given, sin3 x dx= sin2 x ·sin x dx=1 - cos2x · sin x dxu = cos x , du = -sin x dxdx = -1sin x du =1 - u2 · sin x · -1sin x du= -1 - u2 du= -du - u2 du= -u + u33 + C= -cos x + cos3 x3 + C

Problem 11 :

tan3 x dx

Solution :

Given, tan3 x dx= sin3xcos3x dx= sin2xcos3x ·sin x dx= 1 - cos2xcos3 x ·sin x dxu = cos xdu = -sin x dxdx = -dusin x= 1 - u2u3 ·sin x · -dusin x= -1u3 - 1u du= -u-3 - 1u du=--12u-2 - In|u| = 12u2 + In|u|= 12cos2x + In|cos x| + C= 12sec2x + In |cos x| + C

Problem 12 :

sin 7x cos 3x dx

Solution :

Given, sin 7x cos 3x dxsin A cos B = 12[sin (A + B) + sin (A - B)]= 12(sin (7x + 3x) + sin (7x - 3x))dx= 12 sin (10x) + sin (4x) dx= 12 sin 10x + sin 4x dx= 12 sin 10x dx +sin 4x dx = 12 110(-cos 10x) + 14(-cos 4x)= 120(-cos10x) - 18cos 4x= -120cos 10x - 18cos 4x + C

Problem 13 :

sin 10x sin 4x dx

Solution :

Given, sin 10x sin 4x dxsin A sin B = 12[cos (A - B) + cos (A + B)]= 12(cos (10x - 4x) + cos (10x + 4x))dx= 12 cos (6x) + cos (14x)) dx= 12 cos 6x + cos 14x dx= 12 cos 6x dx +cos 14x dx = 12 16sin 6x + 114sin 14x]= 112sin 6x - 128sin 14x= 112sin 6x - 128sin 14x + C

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