I ∫ sec2θ (sec θ + tan θ) . (sec θ + tan θ) dθ Put sec θ + tan θ = y ... (1) ∴ sec θ (tan θ + sec θ) dθ = dy Now, sec θ - tan θ = y1 ... (2) From (1) and (2) , 2 sec θ = y+y1 ∴ I = 21∫y(y+y1) dy = 21[3y3+y] + C = 21[3(secθ+tanθ)3+(secθ+tanθ)] + C = 6secθ+tanθ[(secθ+tanθ)2+3] + C