f'=((3x-2)'*(5x+8)-(3x+2)*(5x+8)')/(5x+8)^2=(3*(5x+8)-(3x+2)*5)/(5x+8)^2=(15x+24-15x-10)/(5x+8)^2=(14)/(5x+8)^2
f'=((3x-2)'*(5x+8)-(3x+2)*(5x+8)')/(5x+8)^2=(3*(5x+8)-(3x+2)*5)/(5x+8)^2=(15x+24-15x-10)/(5x+8)^2=(14)/(5x+8)^2