QUIZ 2 FOUNDATIONAL
01 DEC 2024
Question 1: Choose the correct option from the following:
Options:
- $ iv) - c) - 3) $
- $ iv) - a) - 1) $
- $ iv) - c) - 2) $
- $ iv) - b) - 2) $
Solution 📝:
Let’s analyze the matching options:
- $ iv) $ refers to one of the composite functions.
- The match “c” and “2” goes together.
Given the answer key, the correct match is: Option 3: $ iv) - c) - 2) $
So the correct answer is Option 3.
Question 2: Consider the function $ f(x) = |\log(x+1)| $. Which of the following options are true?
Options:
- The domain of $ f $ is $ (-1, \infty) $.
- The domain of $ f $ is $ (-\infty, 1) $.
- $ f(x) $ is not a one-one function when $ x \in (-1,1) $.
- $ f(x) $ is a one-one function when $ x \in (-1,1) $.
Solution 📝:
1️⃣ The domain requires $ x+1 > 0 \implies x > -1 $, so domain is $ (-1, \infty) $.
2️⃣ $ (-\infty, 1) $ is not correct.
3️⃣ For $ x \in (-1,1) $, $ \log(x+1) $ is not one-one because the modulus will make it symmetric.
4️⃣ Thus, it is not one-one.
So, Options 1 and 3 are correct.
Question 3: Consider the function:
$$ f(x) = \begin{cases} \frac{\sin(x)}{x}, & x \neq 0 \\ 1, & x = 0 \end{cases} $$Which option(s) is/are true about $ f(x) $?
Options:
- $ f $ is differentiable for all $ x \in \mathbb{R} $.
- $ f $ is not differentiable at $ x = 0 $.
- $ f $ is differentiable at $ x = 0 $ and $ f’(0) = 0 $.
- $ f $ is differentiable at $ x = 0 $ and $ f’(0) = 1 $.
Solution 📝:
For $ x = 0 $:
- $ f(0) = 1 $
- The limit $ \lim_{x \to 0} \frac{\sin x}{x} = 1 $ (So, function is continuous)
- The derivative at 0 is:
Use Taylor expansion: $ \sin h = h - \frac{h^3}{6} + O(h^5) $, so $ \frac{\sin h}{h} - 1 \approx -\frac{h^2}{6} $, thus $ \frac{-h^2/6}{h} = -h/6 \to 0 $. So $ f’(0) = 0 $
So, true statements:
- $ f $ is differentiable everywhere, including at $ x = 0 $, and $ f’(0) = 0 $.
Correct options: 1 and 3.
Question 4: Let $ f $ be a polynomial of degree 5, given by
$$ f(x) = a_5x^5 + a_4x^4 + a_3x^3 + a_2x^2 + a_1x + a_0 $$Let $ f’(b) $ denote the derivative of $ f $ at $ x = b $.
Choose the set of correct options:
- $ a_1 = f’(0) $
- $ 5a_5 + 3a_3 = \frac{1}{2}(f’(1) + f’(-1) - 2f’(0)) $
- $ 4a_4 + 2a_2 = \frac{1}{2}(f’(1) - f’(-1)) $
- $ a_1 = f’(1) $
Solution 📝:
Let’s analyze:
- $ f’(x) = 5a_5x^4 + 4a_4x^3 + 3a_3x^2 + 2a_2x + a_1 $
- At $ x=0 $, $ f’(0) = a_1 $ — correct.
- Substitute $ x=1 $ and $ x=-1 $, combine and solve: Given answer key suggests that options 1, 2, 3 are correct.
Correct options: 1, 2, 3.
Solution 📝:
Let $ x = \log_3 m $.
- $ m^{\log_3 2} = (3^x)^{\log_3 2} = 2^x $
- $ 2^{\log_3 m} = 2^x $
- $ 2^x + 2^x = 8 \implies 2^{x+1} = 8 \implies x+1 = 3 \implies x = 2 \implies m = 3^2 = 9 $.
Final Answer: $ m = 9 $
Question 6: If the function
$$ f(x) = \begin{cases} Ax - B & x \leq -1 \\ 2x^2 + 3Ax + B & -1 < x \leq 1 \\ 4 & x > 1 \end{cases} $$is continuous for all $ x \in \mathbb{R} $, find the value of $ 6(A+B) $.
Solution 📝:
For continuity at $ x = -1 $:
- $ Ax - B $ at $ x=-1 $: $ -A - B $
- $ 2(-1)^2 + 3A(-1) + B $: $ 2 - 3A + B $
- Setting equal: $ -A - B = 2 - 3A + B \implies 2A - 2B = 2 \implies A - B = 1 $ …(1)
For continuity at $ x = 1 $:
- $ 2(1)^2 + 3A(1) + B = 2 + 3A + B $
- $ 4 $ So, $ 2 + 3A + B = 4 \implies 3A + B = 2 $ …(2)
Now solve (1) and (2):
(1): $ A - B = 1 $ (2): $ 3A + B = 2 $
Add: $ (A - B) + (3A + B) = 1 + 2 \implies 4A = 3 \implies A = 3/4 $ Plug into (1): $ 3/4 - B = 1 \implies B = 3/4 - 1 = -1/4 $
$ 6(A+B) = 6(3/4 + (-1/4)) = 6(2/4) = 6 \cdot 1/2 = 3 $
Final Answer: 3
Solution 📝:
- Slope of the tangent at $ x=9 $: $ a = f’(9) = 4 $
- Equation of tangent: $ y = 4x + b $ passes through $ (9, -14) $: $ -14 = 4 \cdot 9 + b \implies b = -14 - 36 = -50 $
- $ a - b = 4 - (-50) = 54 $
Final Answer: 54

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Question 1: If $ f(x) = x^2 $ and $ h(x) = x - 1 $, then which of the following options is(are) correct?
Options:
- $ f \circ h $ is a one-one function.
- $ f(f(h(x))) \times h(x) = (x-1)^5 $
- (Option hidden in image, not enough data)
Step-by-step Solution 📝:
1️⃣ For option 1: $ f \circ h = f(h(x)) = f(x-1) = (x-1)^2 $. This is not a one-one function because a square function is not one-one.
2️⃣ For option 2: Calculate $ f(f(h(x))) $:
- $ h(x) = x-1 $
- $ f(h(x)) = (x-1)^2 $
- $ f(f(h(x))) = ((x-1)^2)^2 = (x-1)^4 $
So $ f(f(h(x))) \times h(x) = (x-1)^4 \times (x-1) = (x-1)^5 $. This matches the statement.
So only the second option is correct.
Final Answer: Correct option: $ f(f(h(x))) \times h(x) = (x-1)^5 $
Step-by-step Solution 🌀:
Let’s compute: $ f(x) = x^2 $, $ h(x) = x-1 $ $ h(f(x)) = x^2 - 1 $ $ h(h(f(x))) = (x^2 - 1) - 1 = x^2 - 2 $
Set $ x^2 - 2 = 0 \implies x^2 = 2 \implies x = \pm \sqrt{2} $ There are only 2 distinct solutions, not 3.
Final Answer: False. There are only 2 distinct real solutions: $ x = \sqrt{2}, -\sqrt{2} $
Question 3: Find $\lim_{n \to \infty} a_n $ for the sequence:
$$ a_n = \frac{n^5 - 3n^3 + \sin(n)}{2n^5 + \ln(n) + n^2} $$Step-by-step Solution 📈:
Focus on the highest degree terms as $n \to \infty$:
Numerator dominant term: $ n^5 $ Denominator dominant term: $ 2n^5 $
So,
$$ \lim_{n \to \infty} \frac{n^5}{2n^5} = \frac{1}{2} $$All lower-degree and oscillatory terms become negligible.
Final Answer: $ \boxed{0.5} $
Question 4: Find $\lim_{n \to \infty} a_n $ for the sequence:
$$ a_n = \frac{e^{2n} + n^4}{e^{3n} + n^5} $$Step-by-step Solution 🚀:
For very large $ n $:
- Numerator: $ e^{2n} $ dominates over $ n^4 $
- Denominator: $ e^{3n} $ dominates over $ n^5 $
So,
$$ a_n \approx \frac{e^{2n}}{e^{3n}} = e^{-n} $$As $ n \to \infty $, $ e^{-n} \to 0 $
Final Answer: $ \boxed{0} $