i. x=tan?
so dx/d?=sec^2?
dx=sec^2? d?
substitute it for dx in equation...the equation is
1_x^2/(1+x^2)^2 dx
whch becomes
1_tan^2?/(1+tan^2?)^2 sec^2 ?d?
then put in the identity fr 1+tan^2 ? as sec^2 ?
1-(sec^2?_1)/(sec^2?)^2 *sec^2 ? d?
then we get
2_sec^2?/sec^2? *d?
then
(2/sec^2?) _1 * d?
2cos^2? _1 d?
cos2? d?