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Logarithms Questions and Answers

Important Instructions
101.

Interval used to indicate interval of all integers between a and b is called

Answer: C

An integer interval holds only the whole numbers lying between its endpoints, rather than every real number there:

\[ \{\, x \in \mathbb{Z} : a \le x \le b \,\} \]

So between 2 and 5 it contains 2, 3, 4 and 5, whereas the closed interval \( [2,5] \) contains every real number in that range. Open and closed describe whether the endpoints are included; this option describes which kind of number is included.

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102.

Inverse operation of logarithm is

Answer: D

Logarithm and exponential are inverse operations:

\[ \log_{a}(a^{x}) = x, \qquad a^{\log_{a} x} = x \]

A logarithm asks "to what power?", and exponentiation supplies that power - each undoes the other. Taking antilogs is exactly this exponentiation.

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104.

Laplace transform of function f(t)=cos(wt) is

Answer: C

The standard transform pair is

\[ \mathcal{L}\{\cos \omega t\} = \frac{s}{s^{2}+\omega^{2}} \]

while its companion is

\[ \mathcal{L}\{\sin \omega t\} = \frac{\omega}{s^{2}+\omega^{2}} \]

The denominators are identical; only the numerator distinguishes them - \( s \) for cosine, \( \omega \) for sine.

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105.

The interval \( [a, +\infty) = \{\, x \mid x \geq a \,\} \) is

Answer: D

Read the two features separately.

The square bracket at \( a \) means the endpoint is included (\( x \geq a \)), so the interval is closed at that end. It extends to \( +\infty \) with no upper endpoint, so it is unbounded.

Hence it is closed and unbounded. Infinity is never itself included, which is why that side is always written with a parenthesis.

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106.

A formula or rule for computing derivative of composition of two or more functions is known as

Answer: C

The chain rule differentiates a composition of functions:

\[ \frac{d}{dx}f\big(g(x)\big) = f'\big(g(x)\big) \cdot g'(x) \]

The product rule handles a product of functions, \( (uv)' = u'v + uv' \), which is a different situation entirely.

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107.

If a number has no zero immediately after decimal point, characteristic is

Answer: B

For a number less than 1, the characteristic is negative: it is one more than the number of zeros immediately after the decimal point, taken with a minus sign.

With no such zeros, as in 0.5 or 0.842, the characteristic is \( -1 \), usually written \( \bar{1} \).

\[ \log 0.842 = \bar{1}.9253 = -1 + 0.9253 \]

The mantissa stays positive; only the characteristic carries the sign.

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