Theory of Intelligence
11TH•Mathematics•Functions And Graphs•Question 4

(ii) $g(x) = \sqrt{x + 2}$

Find the domain and the range of the function $g$ defined below:

(ii) g(x)=x+2g(x) = \sqrt{x + 2}

Given:

g(x)=x+2g(x) = \sqrt{x + 2}
  • Domain (DgD_g): For real outputs, require the radicand to be non-negative (x+2≥0  ⟹  x≥−2x + 2 \ge 0 \implies x \ge -2):

    • g(−2)=−2+2=0=0g(-2) = \sqrt{-2 + 2} = \sqrt{0} = 0
    • g(2)=2+2=4=2g(2) = \sqrt{2 + 2} = \sqrt{4} = 2
    • g(7)=7+2=9=3g(7) = \sqrt{7 + 2} = \sqrt{9} = 3
    • For x=−3x = -3: −3+2=−1∉R\sqrt{-3 + 2} = \sqrt{-1} \notin \mathbb{R} (Undefined)
    Dg=[−2,∞)\boxed{D_g = [-2, \infty)}
  • Range (RgR_g): The principal square root produces non-negative outputs:

    y=x+2≥0y = \sqrt{x + 2} \ge 0

    Squaring both sides: y2=x+2  ⟹  x=y2−2≥−2y^2 = x + 2 \implies x = y^2 - 2 \ge -2.

    • Minimum output is 00 at x=−2x = -2.
    • For y=5  ⟹  x=52−2=23  ⟹  g(23)=5y = 5 \implies x = 5^2 - 2 = 23 \implies g(23) = 5.
    Rg=[0,∞)\boxed{R_g = [0, \infty)}
Dg=[−2,∞),Rg=[0,∞)\boxed{D_g = [-2, \infty), \quad R_g = [0, \infty)}

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