How do you write the quadratic in vertex form given #y= -3x^2 + 21x#? Algebra Quadratic Equations and Functions Vertex Form of a Quadratic Equation 1 Answer George C. May 10, 2015 #y = -3(x - 7/2)^2+147/4 = -3(x - 3.5)^2+36.75# #y = -3x^2+21x = -3(x^2-7x)# #= -3((x-(7/2))^2 - (7/2)^2)# #= -3(x-(7/2))^2+3(7/2)^2# #= -3(x - 7/2)^2+147/4# #= -3(x - 3.5)^2+36.75# The vertex of the parabola is #(3.5, 36.75)# Answer link Related questions What is the Vertex Form of a Quadratic Equation? How do you find the vertex form of a quadratic equation? How do you graph quadratic equations written in vertex form? How do you write #y+1=-2x^2-x# in the vertex form? How do you write the quadratic equation given #a=-2# and the vertex #(-5, 0)#? What is the quadratic equation containing (5, 2) and vertex (1, –2)? How do you find the vertex, x-intercept, y-intercept, and graph the equation #y=-4x^2+20x-24#? How do you write #y=9x^2+3x-10# in vertex form? What is the vertex of #y=-1/2(x-4)^2-7#? What is the vertex form of #y=x^2-6x+6#? See all questions in Vertex Form of a Quadratic Equation Impact of this question 1653 views around the world You can reuse this answer Creative Commons License