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Functions question

2022 · 25 Jun · Shift 1 · Q42
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Functions question

2022 · 25 Jun · Shift 1 · Q42

JEE MainMathematicsFunctionsNumerical+4 / −1
Let f:R→Rf:R \to Rf:R→R be a function defined by f(x)=(2(1−x252)(2+x25))150f(x) = {\left( {2\left( {1 - {{{x^{25}}} \over 2}} \right)(2 + {x^{25}})} \right)^{{1 \over {50}}}}f(x)=(2(1−2x25​)(2+x25))501​. If the function g(x)=f(f(f(x)))+f(f(x))g(x) = f(f(f(x))) + f(f(x))g(x)=f(f(f(x)))+f(f(x)), then the greatest integer less than or equal to g(1) is ‾\underline{\hspace{2cm}}​.
Numerical answer
View written solutionFree

Correct answer: 2

  1. Given function

    f(x)=(2(1−x252)(2+x25))1/50f(x)=\left(2\left(1-\frac{x^{25}}{2}\right)(2+x^{25})\right)^{1/50}f(x)=(2(1−2x25​)(2+x25))1/50

    First simplify the expression inside the power.

  2. Simplify the inside

    2(1−x252)=2−x252\left(1-\frac{x^{25}}{2}\right)=2-x^{25}2(1−2x25​)=2−x25

    So, f(x)=((2−x25)(2+x25))1/50f(x)=\left((2-x^{25})(2+x^{25})\right)^{1/50}f(x)=((2−x25)(2+x25))1/50

    Using difference of squares, (2−x25)(2+x25)=4−x50(2-x^{25})(2+x^{25})=4-x^{50}(2−x25)(2+x25)=4−x50

    Hence, f(x)=(4−x50)1/50f(x)=\left(4-x^{50}\right)^{1/50}f(x)=(4−x50)1/50

  3. Compute f(1)f(1)f(1)

    f(1)=(4−150)1/50=31/50f(1)=\left(4-1^{50}\right)^{1/50}=3^{1/50}f(1)=(4−150)1/50=31/50

  4. Compute f(f(1))f(f(1))f(f(1))

    Let a=f(1)=31/50a=f(1)=3^{1/50}a=f(1)=31/50. Then a50=3a^{50}=3a50=3

    Therefore, f(f(1))=f(a)=(4−a50)1/50=(4−3)1/50=1f(f(1))=f(a)=\left(4-a^{50}\right)^{1/50}=\left(4-3\right)^{1/50}=1f(f(1))=f(a)=(4−a50)1/50=(4−3)1/50=1

  5. Compute f(f(f(1)))f(f(f(1)))f(f(f(1)))

    Since f(f(1))=1f(f(1))=1f(f(1))=1, f(f(f(1)))=f(1)=31/50f(f(f(1)))=f(1)=3^{1/50}f(f(f(1)))=f(1)=31/50

  6. Now evaluate g(1)g(1)g(1)

    g(x)=f(f(f(x)))+f(f(x))g(x)=f(f(f(x)))+f(f(x))g(x)=f(f(f(x)))+f(f(x))

    So, g(1)=f(f(f(1)))+f(f(1))=31/50+1g(1)=f(f(f(1)))+f(f(1))=3^{1/50}+1g(1)=f(f(f(1)))+f(f(1))=31/50+1

  7. Find the greatest integer less than or equal to g(1)g(1)g(1)

    Since 31/50>13^{1/50}>131/50>1 and clearly 31/50<2,3^{1/50}<2,31/50<2, we get 2<1+31/50<32<1+3^{1/50}<32<1+31/50<3

    Therefore, ⌊g(1)⌋=2\lfloor g(1)\rfloor=2⌊g(1)⌋=2

  8. Comparison with stored answer

    Derived answer = 222

    Stored correct answer = 222

    They match.

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