How do you write the expression #i ^-18# in the standard form a+ bi? Precalculus Complex Numbers in Trigonometric Form Complex Number Plane 1 Answer Alan P. Feb 12, 2015 #i^(-18) = -1# so #a + bi# becomes #(-1) + (0)i# To see that #i^(-18) = -1# note that #i^1 = sqrt(-1)# #i^0 = 1# #i^-1 =1/(sqrt(-1))# #i^-2 = 1/(-1) = -1# #i^-18 = (i^-2)^9 = (-1)^(9) = -1# Answer link Related questions What is the complex number plane? Which vectors define the complex number plane? What is the modulus of a complex number? How do I graph the complex number #3+4i# in the complex plane? How do I graph the complex number #2-3i# in the complex plane? How do I graph the complex number #-4+2i# in the complex plane? How do I graph the number 3 in the complex number plane? How do I graph the number #4i# in the complex number plane? How do I use graphing in the complex plane to add #2+4i# and #5+3i#? How do I use graphing in the complex plane to subtract #3+4i# from #-2+2i#? See all questions in Complex Number Plane Impact of this question 3944 views around the world You can reuse this answer Creative Commons License