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limx01cosx1+x21x2=\lim_{x \to 0}\frac{1-\cos x}{\sqrt{1+x^{2}}-\sqrt{1-x^{2}}}=\square

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Q. limx01cosx1+x21x2=\lim_{x \to 0}\frac{1-\cos x}{\sqrt{1+x^{2}}-\sqrt{1-x^{2}}}=\square
  1. Identify Problem: We are asked to find the limit of the function (1cosx)/(1+x21x2)(1-\cos x)/(\sqrt{1+x^{2}}-\sqrt{1-x^{2}}) as xx approaches 00. This is a limit problem involving trigonometric and square root functions.
  2. Recognize Indeterminate Form: First, we notice that direct substitution of x=0x = 0 into the function gives us a 0/00/0 indeterminate form. This means we need to apply some algebraic manipulation or a limit law to evaluate the limit.
  3. Apply Algebraic Manipulation: To resolve the indeterminate form, we can multiply the numerator and the denominator by the conjugate of the denominator. The conjugate of 1+x21x2\sqrt{1+x^{2}}-\sqrt{1-x^{2}} is 1+x2+1x2\sqrt{1+x^{2}}+\sqrt{1-x^{2}}.
  4. Multiply by Conjugate: Multiplying the numerator and denominator by the conjugate, we get: limx0(1cosx)(1+x2+1x2)(1+x21x2)(1+x2+1x2)\lim_{x \rightarrow 0} \frac{(1-\cos x)(\sqrt{1+x^{2}}+\sqrt{1-x^{2}})}{(\sqrt{1+x^{2}}-\sqrt{1-x^{2}})(\sqrt{1+x^{2}}+\sqrt{1-x^{2}})}
  5. Simplify Denominator: Simplify the denominator using the difference of squares formula: (ab)(a+b)=a2b2(a-b)(a+b) = a^2 - b^2. This gives us:\newlinelimx0(1cosx)(1+x2+1x2)(1+x2)(1x2)\lim_{x \to 0} \frac{(1-\cos x)(\sqrt{1+x^{2}}+\sqrt{1-x^{2}})}{(1+x^{2}) - (1-x^{2})}
  6. Combine Like Terms: Simplify the denominator further: limx0(1cosx)(1+x2+1x2)1+x21+x2\lim_{x \rightarrow 0} \frac{(1-\cos x)(\sqrt{1+x^{2}}+\sqrt{1-x^{2}})}{1+x^{2} - 1 + x^{2}}
  7. Distribute and Simplify Numerator: Combine like terms in the denominator: limx0(1cosx)(1+x2+1x2)2x2\lim_{x \rightarrow 0} \frac{(1-\cos x)(\sqrt{1+x^{2}}+\sqrt{1-x^{2}})}{2x^{2}}
  8. Evaluate Each Term: Now, we can simplify the numerator by distributing (1cosx)(1-\cos x) over the sum inside the square roots: limx0(1cosx)1+x2+(1cosx)1x22x2\lim_{x \to 0} \frac{(1-\cos x)\sqrt{1+x^{2}} + (1-\cos x)\sqrt{1-x^{2}}}{2x^{2}}
  9. Correct Error and Re-evaluate: We can now evaluate the limit of each term separately as xx approaches 00. For the first term, (1cosx)1+x2(1-\cos x)\sqrt{1+x^{2}}, as xx approaches 00, (1cosx)(1-\cos x) approaches 00 and 1+x2\sqrt{1+x^{2}} approaches 11. For the second term, (1cosx)1x2(1-\cos x)\sqrt{1-x^{2}}, as xx approaches 00, (1cosx)(1-\cos x) approaches 00 and 0044 approaches 11.
  10. Correct Error and Re-evaluate: We can now evaluate the limit of each term separately as xx approaches 00. For the first term, (1cosx)1+x2(1-\cos x)\sqrt{1+x^{2}}, as xx approaches 00, (1cosx)(1-\cos x) approaches 00 and 1+x2\sqrt{1+x^{2}} approaches 11. For the second term, (1cosx)1x2(1-\cos x)\sqrt{1-x^{2}}, as xx approaches 00, (1cosx)(1-\cos x) approaches 00 and 0044 approaches 11.However, we realize that there is a mistake in the previous step. The limit of (1cosx)(1-\cos x) as xx approaches 00 is not 00, but rather (1cosx)1+x2(1-\cos x)\sqrt{1+x^{2}}00. This means that the numerator approaches 00 as xx approaches 00. We need to correct this error and re-evaluate the limit.

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