Theory of Intelligence
11TH•Mathematics•Theory Of Quadratic Functions•Question 2

Step-by-Step Solution

Find the maximum or minimum point by sketching the following quadratic functions. Also find their domain and range:

Step-by-Step Solution

Step 1: Identify Parameters and Vertex

For f(x)=ax2+bx+cf(x) = ax^2 + bx + c:

a=1,b=−5,c=6a = 1, \quad b = -5, \quad c = 6

Since a=1>0a = 1 > 0, the parabola opens upwards, so the vertex is an absolute minimum point.

The xx-coordinate of the vertex hh:

h=−b2a=−−52(1)=52=2.5h = -\frac{b}{2a} = -\frac{-5}{2(1)} = \frac{5}{2} = 2.5

The yy-coordinate kk:

k=f(52)=(52)2−5(52)+6=254−252+6=−254+244=−14=−0.25k = f\left(\frac{5}{2}\right) = \left(\frac{5}{2}\right)^2 - 5\left(\frac{5}{2}\right) + 6 = \frac{25}{4} - \frac{25}{2} + 6 = -\frac{25}{4} + \frac{24}{4} = -\frac{1}{4} = -0.25

The vertex point is (52,−14)\left(\frac{5}{2}, -\frac{1}{4}\right).

Step 2: Intercepts & Axis of Symmetry

  • yy-intercept: f(0)=6  ⟹  (0,6)f(0) = 6 \implies (0, 6).
  • xx-intercepts: Factor x2−5x+6=(x−2)(x−3)=0  ⟹  x=2x^2 - 5x + 6 = (x - 2)(x - 3) = 0 \implies x = 2 and x=3x = 3.
  • Axis of Symmetry: x=52=2.5x = \frac{5}{2} = 2.5

Step 3: Domain and Range

  • Domain: All quadratic polynomials are defined everywhere on the real line: Domain=R=(−∞,∞)\text{Domain} = \mathbb{R} = (-\infty, \infty)
  • Range: Since the vertex is the absolute minimum at y=−0.25y = -0.25: Range=[−14,∞)=[−0.25,∞)\text{Range} = \left[-\frac{1}{4}, \infty\right) = [-0.25, \infty)

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