How do you find #abs( -3+4i)#? Precalculus Complex Numbers in Trigonometric Form Complex Number Plane 1 Answer Trevor Ryan. Mar 30, 2016 #|-3+4i|=sqrt((-3)^2+4^2)=5# Explanation: Let #z=x+iy# be any complex number in rectangular form. Then its modulus is given by #|z|=sqrt(x^2+y^2)#. So in this case we get #|-3+4i|=sqrt((-3)^2+4^2)=sqrt25=5# 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 1642 views around the world You can reuse this answer Creative Commons License