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

(iii) $g(x) = \begin{cases} 6x + 7, & x \le -2 \\ 4 - 3x, & x > -2 \end{cases}$

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

(iii) g(x)={6x+7,x≤−24−3x,x>−2g(x) = \begin{cases} 6x + 7, & x \le -2 \\ 4 - 3x, & x > -2 \end{cases}

Given:

g(x)={6x+7,x≤−24−3x,x>−2g(x) = \begin{cases} 6x + 7, & x \le -2 \\ 4 - 3x, & x > -2 \end{cases}
  • Domain (DgD_g): Both intervals combine to cover all real numbers:

    • For x≤−2x \le -2: g(−2)=6(−2)+7=−5g(-2) = 6(-2) + 7 = -5, g(−3)=6(−3)+7=−11g(-3) = 6(-3) + 7 = -11
    • For x>−2x > -2: g(0)=4−3(0)=4g(0) = 4 - 3(0) = 4, g(2)=4−3(2)=−2g(2) = 4 - 3(2) = -2
    Dg=(−∞,−2]∪(−2,∞)=RD_g = (-\infty, -2] \cup (-2, \infty) = \mathbb{R} Dg=R=(−∞,∞)\boxed{D_g = \mathbb{R} = (-\infty, \infty)}
  • Range (RgR_g):

    • For x≤−2x \le -2: g(x)≤6(−2)+7=−5  ⟹  (−∞,−5]g(x) \le 6(-2) + 7 = -5 \implies (-\infty, -5]
    • For x>−2x > -2: g(x)<4−3(−2)=10  ⟹  (−∞,10)g(x) < 4 - 3(-2) = 10 \implies (-\infty, 10) Combined range:
    Rg=(−∞,−5]∪(−∞,10)=(−∞,10)R_g = (-\infty, -5] \cup (-\infty, 10) = (-\infty, 10) Rg=(−∞,10)\boxed{R_g = (-\infty, 10)}
Dg=R,Rg=(−∞,10)\boxed{D_g = \mathbb{R}, \quad R_g = (-\infty, 10)}

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