#2 d/dx sec[sqrt(3x+1)]#
#=2 {[secsqrt(3x+1)]*[tansqrt(3x+1)]}*d/dx [sqrt(3x+1)]}#
#=2*{[sec sqrt(3x+1)]*[tan sqrt(3x+1)]}*{1/[2(sqrt (3x+1)]}*d/dx(3x+1)}#
#=2*{[sec sqrt(3x+1)]*[tan sqrt(3x+1)]}*[1/[2(sqrt (3x+1)]]*(3(1)+0)}#
#=2*{[sec sqrt(3x+1)]*[tan sqrt(3x+1)]}*{1/[2*sqrt (3x+1)]}*3#