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Functions question

2023 · 24 Jan · Shift 2 · Q31
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  5. /2023 · 24 Jan · Shift 2 · Q31

Functions question

2023 · 24 Jan · Shift 2 · Q31

JEE MainMathematicsFunctionsMCQ+4 / −1
If f(x)=22x22x+2,x∈Rf(x) = {{{2^{2x}}} \over {{2^{2x}} + 2}},x \in \mathbb{R}f(x)=22x+222x​,x∈R, then f(12023)+f(22023) + ... + f(20222023)f\left( {{1 \over {2023}}} \right) + f\left( {{2 \over {2023}}} \right)\, + \,...\, + \,f\left( {{{2022} \over {2023}}} \right)f(20231​)+f(20232​)+...+f(20232022​) is equal to
  1. A
    2011
  2. B
    2010
  3. C
    1010
  4. D
    1011
View written solutionFree

Correct answer: D

  1. We are given
f(x)=22x22x+2.f(x)=\frac{2^{2x}}{2^{2x}+2}.f(x)=22x+222x​.

Let

S=f(12023)+f(22023)+⋯+f(20222023).S=f\left(\frac1{2023}\right)+f\left(\frac2{2023}\right)+\cdots+f\left(\frac{2022}{2023}\right).S=f(20231​)+f(20232​)+⋯+f(20232022​).
  1. First, simplify the function a little:
22x=4x.2^{2x}=4^x.22x=4x.

So

f(x)=4x4x+2.f(x)=\frac{4^x}{4^x+2}.f(x)=4x+24x​.
  1. Now compute f(1−x)f(1-x)f(1−x):
f(1−x)=41−x41−x+2.f(1-x)=\frac{4^{1-x}}{4^{1-x}+2}.f(1−x)=41−x+241−x​.

Since 41−x=44x4^{1-x}=\frac{4}{4^x}41−x=4x4​, we get

f(1−x)=44x44x+2.f(1-x)=\frac{\frac{4}{4^x}}{\frac{4}{4^x}+2}.f(1−x)=4x4​+24x4​​.

Multiply numerator and denominator by 4x4^x4x:

f(1-x)=\frac{4}{4+2\cdot 4^x}= rac{2}{2+4^x}.

Also,

f(x)=4x4x+2.f(x)=\frac{4^x}{4^x+2}.f(x)=4x+24x​.

Hence,

f(x)+f(1−x)=4x4x+2+24x+2=1.f(x)+f(1-x)=\frac{4^x}{4^x+2}+\frac{2}{4^x+2}=1.f(x)+f(1−x)=4x+24x​+4x+22​=1.
  1. In the required sum, terms pair up as:
f(k2023)+f(1−k2023)=f(k2023)+f(2023−k2023)=1.f\left(\frac{k}{2023}\right)+f\left(1-\frac{k}{2023}\right) =f\left(\frac{k}{2023}\right)+f\left(\frac{2023-k}{2023}\right)=1.f(2023k​)+f(1−2023k​)=f(2023k​)+f(20232023−k​)=1.
  1. The values of kkk run from 111 to 202220222022. So the terms can be paired as:
(12023,20222023),(22023,20212023),…\left(\frac1{2023},\frac{2022}{2023}\right), \left(\frac2{2023},\frac{2021}{2023}\right), \dots(20231​,20232022​),(20232​,20232021​),…

There are

20222=1011\frac{2022}{2}=101122022​=1011

such pairs.

  1. Each pair sums to 111, so
S=1011.S=1011.S=1011.
  1. Therefore the correct option is
D: 1011.\boxed{\text{D: }1011}.D: 1011​.
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