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The number of integers xx such that 0.25<2x<2000.25 < 2^x < 200, and 2x+22^x + 2 is perfectly divisible by either 33 or 44, is

Entered answer:

Solution

✅ Correct Answer: 5

We need to find integer values of xx that satisfy two conditions:

  1. 0.25<2x<2000.25 < 2^x < 200
  2. 2x+22^x + 2 is divisible by either 3 or 4

First, we'll convert 0.25 to a power of 2:

0.25=14=2−20.25 = \frac{1}{4} = 2^{-2}

So the inequality becomes:

2−2<2x<2002^{-2} < 2^x < 200

For the left side: 2−2<2x2^{-2} < 2^x

Since the exponential function 2x2^x is increasing, this means:

−2<x-2 < x, so x>−2x > -2

For the right side: 2x<2002^x < 200

Let us check some powers of 2:

  • 27=128<2002^7 = 128 < 200
  • 28=256>2002^8 = 256 > 200

So we need x≤7x ≤ 7 (since xx must be an integer)

Combining both conditions: −2<x≤7-2 < x ≤ 7

Since xx must be an integer: x∈{−1,0,1,2,3,4,5,6,7}x \in \{-1, 0, 1, 2, 3, 4, 5, 6, 7\}


Now we'll calculate 2x+22^x + 2 for each possible value of xx:

x=−1x = -1: 2−1+2=0.5+2=2.52^{-1} + 2 = 0.5 + 2 = 2.5

Since this isn't an integer, it can't be divisible by 3 or 4.

x=0x = 0: 20+2=1+2=32^0 + 2 = 1 + 2 = 3

3÷3=13 ÷ 3 = 1 (divisible by 3)

x=1x = 1: 21+2=2+2=42^1 + 2 = 2 + 2 = 4

4÷4=14 ÷ 4 = 1 (divisible by 4)

x=2x = 2: 22+2=4+2=62^2 + 2 = 4 + 2 = 6

6÷3=26 ÷ 3 = 2 (divisible by 3)

x=3x = 3: 23+2=8+2=102^3 + 2 = 8 + 2 = 10

10÷3=3.33...10 ÷ 3 = 3.33... and 10÷4=2.510 ÷ 4 = 2.5 (not divisible by 3 or 4)

x=4x = 4: 24+2=16+2=182^4 + 2 = 16 + 2 = 18

18÷3=618 ÷ 3 = 6 (divisible by 3)

x=5x = 5: 25+2=32+2=342^5 + 2 = 32 + 2 = 34

34÷3=11.33...34 ÷ 3 = 11.33... and 34÷4=8.534 ÷ 4 = 8.5 (not divisible by 3 or 4)

x=6x = 6: 26+2=64+2=662^6 + 2 = 64 + 2 = 66

66÷3=2266 ÷ 3 = 22 (divisible by 3)

x=7x = 7: 27+2=128+2=1302^7 + 2 = 128 + 2 = 130

130÷3=43.33...130 ÷ 3 = 43.33... and 130÷4=32.5130 ÷ 4 = 32.5 (not divisible by 3 or 4)


The values of xx that satisfy both conditions are: x∈{0,1,2,4,6}x \in \{0, 1, 2, 4, 6\}

The number of integers xx is 5.

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