I have this function: f(x) = (4x-3)/(x² + 1) (upper limit is 3/4, lower limit is 0)

i have trouble integrating it; if it were simply f(x) = 4x/(x² +1) then that would be easy but the -3 causes problems...

in my solutions it has a really strange explanation of "argtgx" which i have never seen before, help very very appreciated please!