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A parabola graphed in the 
xy-plane has equation 
y=-3x^(2)+9x-2. What is the 
y-coordinate of the vertex of the parabola?

A parabola graphed in the xy x y -plane has equation y=3x2+9x2 y=-3 x^{2}+9 x-2 . What is the y y -coordinate of the vertex of the parabola?

Full solution

Q. A parabola graphed in the xy x y -plane has equation y=3x2+9x2 y=-3 x^{2}+9 x-2 . What is the y y -coordinate of the vertex of the parabola?
  1. Write quadratic equation: Write down the given quadratic equation.\newlineThe given quadratic equation is y=3x2+9x2y = -3x^2 + 9x - 2.
  2. Convert to vertex form: Convert the quadratic equation into vertex form.\newlineThe vertex form of a quadratic equation is y=a(xh)2+ky = a(x - h)^2 + k, where (h,k)(h, k) is the vertex of the parabola.\newlineTo convert the given equation into vertex form, we need to complete the square.
  3. Factor out xx terms: Factor out the coefficient of x2x^2 from the xx terms.\newlineFactor out 3-3 from 3x2-3x^2 and 9x9x.\newliney=3(x23x)2y = -3(x^2 - 3x) - 2
  4. Find (b/2)2(b/2)^2: Find the value of (b/2)2(b/2)^2 for x23xx^2 - 3x. The coefficient of xx is 3-3. (3/2)2=(1.5)2=2.25(-3/2)^2 = (-1.5)^2 = 2.25
  5. Complete the square: Add and subtract (b2)2(\frac{b}{2})^2 inside the parentheses to complete the square.\newliney=3(x23x+2.252.25)2y = -3(x^2 - 3x + 2.25 - 2.25) - 2\newliney=3((x23x+2.25)2.25)2y = -3((x^2 - 3x + 2.25) - 2.25) - 2
  6. Rewrite as perfect square trinomial: Rewrite the equation as a perfect square trinomial.\newliney=3((x1.5)22.25)2y = -3((x - 1.5)^2 - 2.25) - 2
  7. Distribute and simplify: Distribute the 3-3 and simplify the equation.\newliney=3(x1.5)2+6.752y = -3(x - 1.5)^2 + 6.75 - 2\newliney=3(x1.5)2+4.75y = -3(x - 1.5)^2 + 4.75
  8. Identify the vertex: Identify the vertex of the parabola.\newlineThe vertex form of the equation is now y=3(x1.5)2+4.75y = -3(x - 1.5)^2 + 4.75, so the vertex is at (h,k)=(1.5,4.75)(h, k) = (1.5, 4.75).\newlineThe yy-coordinate of the vertex is 4.754.75.

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