The function g is defined by , for , .
- (a)
Explain how you know exists.
- (b)
Find and write down its domain.
- (c)
Solve exactly.
- (d)
Hence, without using a calculator, solve the inequality
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Worked solution
8(a)
1. Show algebraically that the function is one-to-one.
Let for .
Since strictly implies , the function is a one-to-one function.
2. State the conclusion linking the one-to-one property to the existence of an inverse.
An inverse function exists if and only if the function is one-to-one. Therefore, exists.
Since , is a one-to-one function. Therefore, exists.
8(b)
1. Set up an equation and make $x$ the subject to find the inverse function.
Let .
2. State the inverse function in terms of $x$.
3. Determine the domain of $g^{-1}$ by evaluating the range of $g$.
The domain of is the range of .
Given the domain of is , the expression takes all positive real values.
Therefore, the range of is all real numbers.
Domain of is .
, Domain:
8(c)
1. Set the function to zero and convert the logarithmic equation to an exponential equation.
2. Solve for $x$ and state the exact value.
8(d)
1. Find the critical values from the numerator and denominator.
First, we concisely reproduce the result of part (c) by solving :
Next, we find the critical values of the denominator by setting it to zero:
2. Analyse the sign of the rational expression within the domain of the function.
The domain of is given as . Therefore, is rejected since it falls outside the domain, and we note that for all valid .
We test the signs of the expression across the intervals defined by the valid critical values and :
- For : and , so the expression is positive.
- For : and , so the expression is negative.
- For : and , so the expression is positive.
3. State the final solution for the inequality.
The inequality requires the rational expression to be greater than or equal to .
At , the numerator is , making the expression exactly , which satisfies the inequality. At , the expression is undefined.
Combining this with the sign analysis, we obtain the final solution:
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