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Question
Math
Posted 6 months ago
Is the function f(x)=(x-3)/(x^2 +9x -22) injective and surjective?
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Answer from Sia
Posted 6 months ago
Solution by Steps
step 1
To determine if the function f(x)=x3x2+9x22f(x) = \frac{x-3}{x^2 + 9x - 22} is injective, we need to check if f(x1)=f(x2)f(x_1) = f(x_2) implies x1=x2x_1 = x_2
step 2
Let f(x1)=f(x2)f(x_1) = f(x_2). Then, x13x12+9x122=x23x22+9x222\frac{x_1 - 3}{x_1^2 + 9x_1 - 22} = \frac{x_2 - 3}{x_2^2 + 9x_2 - 22}
step 3
Cross-multiplying gives (x13)(x22+9x222)=(x23)(x12+9x122)(x_1 - 3)(x_2^2 + 9x_2 - 22) = (x_2 - 3)(x_1^2 + 9x_1 - 22)
step 4
Expanding and simplifying this equation does not necessarily lead to x1=x2x_1 = x_2, indicating that f(x)f(x) is not injective
step 5
To determine if the function is surjective, we need to check if for every yRy \in \mathbb{R}, there exists an xRx \in \mathbb{R} such that f(x)=yf(x) = y
step 6
The function f(x)=x3x2+9x22f(x) = \frac{x-3}{x^2 + 9x - 22} is not surjective onto R\mathbb{R} because there are values of yy for which no xx satisfies the equation y=x3x2+9x22y = \frac{x-3}{x^2 + 9x - 22}
step 7
Specifically, the range of f(x)f(x) is restricted by the conditions 169y+21415169y + 2\sqrt{14} \leq 15 or 169y15+214169y \geq 15 + 2\sqrt{14}
Answer
The function f(x)=x3x2+9x22f(x) = \frac{x-3}{x^2 + 9x - 22} is neither injective nor surjective.
Key Concept
Injectivity and Surjectivity of Rational Functions
Explanation
A function is injective if each element of the function's codomain is mapped by at most one element of its domain. It is surjective if every element of the codomain is mapped by at least one element of its domain. The given function fails both criteria.

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