What is the vertex of #y= -x^2+16x + 21#? Algebra Quadratic Equations and Functions Quadratic Functions and Their Graphs 1 Answer Mark D. Jun 30, 2018 (8,85) Explanation: #(-b)/(2a)# gives the x coordinate for the vertex #(-16)/(2xx-1)=(-16)/(-2)=8# Put x=8 into the equation #y=-8^2+16xx8+21# #y=-64+128+21# #y=85# 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 1300 views around the world You can reuse this answer Creative Commons License