Let's perform the long division
color(white)(aaaa)2x^2+1color(white)(aaaa)|6x^3+10x^2+x+8color(white)(aaaa)|3x+5
color(white)(aaaaaaaaaaaaaaaa)6x^3color(white)(aa aaaaa)+3xcolor(white)(aaaa)
color(white)(aaaaaaaaaaaaaaaaa)0color(white)(aa aa)10x^2-2xcolor(white)(aaaa)
color(white)(aaaaaaaaaaaaaaaaa)color(white)(aa aaa)10x^2color(white)(aaaa)+5color(white)(aaaa)
color(white)(aaaaaaaaaaaaaaaaa)color(white)(aa aaaa)0color(white)(aaaaaa)+3color(white)(aaaa)
color(white)(aaaaaaaaaaaaaaaaa)color(white)(aa aaaaaa)-2xcolor(white)(aa)+3color(white)(aaaa)
(6x^3+10x^2+x+8)/(2x^2+1)=(3x+5)+(-2x+3)/(2x^2+1)