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दो हजार बारह - (हिंदी अक्षरों को पढ़कर संख्याओं को विकल्पों में से पहचानकर लिखिए ।)

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6 parts
21

12a\dfrac{1}{2\sqrt{a}}

22

13\dfrac{1}{3}

24

32\dfrac{3}{2}

25

16\dfrac{1}{6}

26

12\dfrac{1}{2}

Step-by-step solution

22 steps

Part 21· 4 steps

  1. Write the given limit.

    lim⁡x→ax−ax−a\lim_{x \to a} \frac{\sqrt{x} - \sqrt{a}}{x - a}
  2. Multiply numerator and denominator by the conjugate x+a\sqrt{x} + \sqrt{a}.

    lim⁡x→a(x−a)(x+a)(x−a)(x+a)=lim⁡x→ax−a(x−a)(x+a)\lim_{x \to a} \frac{(\sqrt{x} - \sqrt{a})(\sqrt{x} + \sqrt{a})}{(x - a)(\sqrt{x} + \sqrt{a})} = \lim_{x \to a} \frac{x - a}{(x - a)(\sqrt{x} + \sqrt{a})}
  3. Cancel the common factor x−ax - a (valid as x≠ax \neq a in the limit).

    lim⁡x→a1x+a\lim_{x \to a} \frac{1}{\sqrt{x} + \sqrt{a}}
  4. Substitute x=ax = a.

    1a+a=12a\frac{1}{\sqrt{a} + \sqrt{a}} = \frac{1}{2\sqrt{a}}

    \dfrac{1}{2\sqrt{a}}

Part 22

13\dfrac{1}{3}

  1. Rewrite tan⁡x=sin⁡xcos⁡x\tan x = \frac{\sin x}{\cos x}.

    lim⁡x→0tan⁡x−xx3=lim⁡x→0sin⁡xcos⁡x−xx3=lim⁡x→0sin⁡x−xcos⁡xx3cos⁡x\lim_{x \to 0} \frac{\tan x - x}{x^3} = \lim_{x \to 0} \frac{\frac{\sin x}{\cos x} - x}{x^3} = \lim_{x \to 0} \frac{\sin x - x \cos x}{x^3 \cos x}
  2. Since lim⁡x→0cos⁡x=1\lim_{x \to 0} \cos x = 1, the limit is lim⁡x→0sin⁡x−xcos⁡xx3\lim_{x \to 0} \frac{\sin x - x \cos x}{x^3}.

  3. Use Taylor expansions around x=0x = 0

    sin⁡x=x−x36+o(x3),cos⁡x=1−x22+o(x4)\sin x = x - \frac{x^3}{6} + o(x^3), \quad \cos x = 1 - \frac{x^2}{2} + o(x^4)
  4. Compute xcos⁡xx \cos x

    xcos⁡x=x(1−x22+o(x4))=x−x32+o(x5)x \cos x = x \left(1 - \frac{x^2}{2} + o(x^4)\right) = x - \frac{x^3}{2} + o(x^5)
  5. Numerator sin⁡x−xcos⁡x\sin x - x \cos x

    (x−x36+o(x3))−(x−x32+o(x5))=−x36+x32+o(x3)=(12−16)x3+o(x3)=13x3+o(x3)\left(x - \frac{x^3}{6} + o(x^3)\right) - \left(x - \frac{x^3}{2} + o(x^5)\right) = -\frac{x^3}{6} + \frac{x^3}{2} + o(x^3) = \left(\frac{1}{2} - \frac{1}{6}\right)x^3 + o(x^3) = \frac{1}{3}x^3 + o(x^3)
  6. Divide by x3x^3

    lim⁡x→013x3+o(x3)x3=13\lim_{x \to 0} \frac{\frac{1}{3}x^3 + o(x^3)}{x^3} = \frac{1}{3}

    \dfrac{1}{3}

Part 231

  1. Substitute t=π2−xt = \frac{\pi}{2} - x.

    As x→π2x \to \frac{\pi}{2}, t→0t \to 0.

    lim⁡x→π2(π2−x)tan⁡x=lim⁡t→0ttan⁡(π2−t)=lim⁡t→0tcot⁡t\lim_{x \to \frac{\pi}{2}} \left(\frac{\pi}{2} - x\right) \tan x = \lim_{t \to 0} t \tan\left(\frac{\pi}{2} - t\right) = \lim_{t \to 0} t \cot t
  2. Rewrite cot⁡t=1tan⁡t\cot t = \frac{1}{\tan t}.

    tcot⁡t=ttan⁡t=tcos⁡tsin⁡tt \cot t = \frac{t}{\tan t} = \frac{t \cos t}{\sin t}
  3. lim⁡t→0tcos⁡tsin⁡t=lim⁡t→0(tsin⁡t⋅cos⁡t)=(lim⁡t→0tsin⁡t)(lim⁡t→0cos⁡t)=1⋅1=1\lim_{t \to 0} \frac{t \cos t}{\sin t} = \lim_{t \to 0} \left( \frac{t}{\sin t} \cdot \cos t \right) = \left( \lim_{t \to 0} \frac{t}{\sin t} \right) \left( \lim_{t \to 0} \cos t \right) = 1 \cdot 1 = 1

    1

Part 24

32\dfrac{3}{2}

  1. Factor the numerator using 1−u3=(1−u)(1+u+u2)1 - u^3 = (1 - u)(1 + u + u^2) where u=cos⁡xu = \cos x.

    1−cos⁡3x=(1−cos⁡x)(1+cos⁡x+cos⁡2x)1 - \cos^3 x = (1 - \cos x)(1 + \cos x + \cos^2 x) lim⁡x→01−cos⁡3xx2=lim⁡x→0(1−cos⁡x)(1+cos⁡x+cos⁡2x)x2=lim⁡x→0[1−cos⁡xx2⋅(1+cos⁡x+cos⁡2x)]\lim_{x \to 0} \frac{1 - \cos^3 x}{x^2} = \lim_{x \to 0} \frac{(1 - \cos x)(1 + \cos x + \cos^2 x)}{x^2} = \lim_{x \to 0} \left[ \frac{1 - \cos x}{x^2} \cdot (1 + \cos x + \cos^2 x) \right]
  2. Evaluate each limit separately.

    lim⁡x→01−cos⁡xx2=12,lim⁡x→0(1+cos⁡x+cos⁡2x)=1+1+12=3\lim_{x \to 0} \frac{1 - \cos x}{x^2} = \frac{1}{2}, \quad \lim_{x \to 0} (1 + \cos x + \cos^2 x) = 1 + 1 + 1^2 = 3
  3. Multiply the limits.

    12×3=32\frac{1}{2} \times 3 = \frac{3}{2}

    \dfrac{3}{2}

Part 25

16\dfrac{1}{6}

  1. Use Taylor expansion for sin⁡x\sin x around x=0x = 0.

    sin⁡x=x−x36+o(x3)\sin x = x - \frac{x^3}{6} + o(x^3)
  2. Numerator x−sin⁡xx - \sin x

    x−sin⁡x=x−(x−x36+o(x3))=x36+o(x3)x - \sin x = x - \left(x - \frac{x^3}{6} + o(x^3)\right) = \frac{x^3}{6} + o(x^3)
  3. Divide by x3x^3

    lim⁡x→0x−sin⁡xx3=lim⁡x→0x36+o(x3)x3=16\lim_{x \to 0} \frac{x - \sin x}{x^3} = \lim_{x \to 0} \frac{\frac{x^3}{6} + o(x^3)}{x^3} = \frac{1}{6}

    \dfrac{1}{6}

Part 26

12\dfrac{1}{2}

  1. Rewrite tan⁡x−sin⁡x\tan x - \sin x.

    tan⁡x−sin⁡x=sin⁡xcos⁡x−sin⁡x=sin⁡x(1cos⁡x−1)=sin⁡x⋅1−cos⁡xcos⁡x\tan x - \sin x = \frac{\sin x}{\cos x} - \sin x = \sin x \left( \frac{1}{\cos x} - 1 \right) = \sin x \cdot \frac{1 - \cos x}{\cos x} lim⁡x→0tan⁡x−sin⁡xx3=lim⁡x→0sin⁡x(1−cos⁡x)x3cos⁡x=lim⁡x→0[sin⁡xx⋅1−cos⁡xx2⋅1cos⁡x]\lim_{x \to 0} \frac{\tan x - \sin x}{x^3} = \lim_{x \to 0} \frac{\sin x (1 - \cos x)}{x^3 \cos x} = \lim_{x \to 0} \left[ \frac{\sin x}{x} \cdot \frac{1 - \cos x}{x^2} \cdot \frac{1}{\cos x} \right]
  2. Evaluate each limit separately.

    lim⁡x→0sin⁡xx=1,lim⁡x→01−cos⁡xx2=12,lim⁡x→01cos⁡x=1\lim_{x \to 0} \frac{\sin x}{x} = 1, \quad \lim_{x \to 0} \frac{1 - \cos x}{x^2} = \frac{1}{2}, \quad \lim_{x \to 0} \frac{1}{\cos x} = 1
  3. Multiply the limits.

    1⋅12⋅1=121 \cdot \frac{1}{2} \cdot 1 = \frac{1}{2}

    \dfrac{1}{2}

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