y'=[cos^2(x^2+1)]'
=[2cos(x^2+1)]·[cos(x^2+1)]'
=[2cos(x^2+1)]·[-sin(x^2+1)]·[x^2+1]'
=[2cos(x^2+1)]·[-sin(x^2+1)]·2x
中间用的都是链导法则