[" 13.The value of "sum_(n=1)^(11)(i^(n)+i^(n+1))" equals to "],[[" 1) "i-1," 2) "i+1," 3) "-i+1],[" 14."," If "z" is a complex number of unit modulus and argument "theta" then "arg((1+z)/(1+z))" is equal to "]]