1) Let In=∫tannxdx(n>1),If I4+I6=atan5x+bx5+C, , where C is a constant of integration, then orderd pair (a,b) is equal to A) (−15,1) B) (15,0) C) (15,−1) D) (−15,0) Answer: Option BExplanation:We have, In=∫tannxdx ∴In+In+2=∫tannxdx+∫tannxdx =∫tannx(1+tan2x)dx =∫tannxsec2xdx =tann+1xn+1+C Put n=4, we get I4+I6=tan5x5+C ∴a=15 and b=0