How do you solve for #x# in #y = 4x - x^2#? Algebra Quadratic Equations and Functions Quadratic Functions and Their Graphs 1 Answer Noah G Jan 5, 2017 #y = -(x^2 - 4x)# #y = -(x^2 - 4x + 4 - 4)# #y = -(x- 2)^2 + 4# You can solve for #x# now: #y - 4 = -(x - 2)^2# #4 - y = (x - 2)^2# #+-sqrt(4 - y) = x - 2# #2+-sqrt(y - 4) = x# Hopefully this helps! Answer link Related questions What are the important features of the graphs of quadratic functions? What do quadratic function graphs look like? How do you find the x intercepts of a quadratic function? How do you determine the vertex and direction when given a quadratic function? How do you determine the range of a quadratic function? What is the domain of quadratic functions? How do you find the maximum or minimum of quadratic functions? How do you graph #y=x^2-2x+3#? How do you know if #y=16-4x^2# opens up or down? How do you find the x-coordinate of the vertex for the graph #4x^2+16x+12=0#? See all questions in Quadratic Functions and Their Graphs Impact of this question 11732 views around the world You can reuse this answer Creative Commons License