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For all possible integers nn satisfying 2.25≤2+2n+2≤2022.25 \leq 2+2^{n+2} \leq 202, the number of integer values of 3+3n+13+3^{n+1} is

Entered answer:

Solution

✅ Correct Answer: 7

Given: 2.25≤2+2n+2≤2022.25 \leq 2+2^{n+2} \leq 202

We isolate the exponential term:

0.25≤2n+2≤2000.25 \leq 2^{n+2} \leq 200

Key insight: 0.25=14=122=2−20.25 = \tfrac{1}{4} = \tfrac{1}{2^2} = 2^{-2}

So our inequality becomes:

2−2≤2n+2≤2002^{-2} \leq 2^{n+2} \leq 200


For the left inequality: 2−2≤2n+22^{-2} \leq 2^{n+2}

Since the exponential function 2x2^x is increasing, we can compare exponents directly:

−2≤n+2-2 \leq n+2

Therefore: n≥−4n \geq -4

For the right inequality: 2n+2≤2002^{n+2} \leq 200

We need: n+2≤log⁡2(200)n+2 \leq \log_2(200)

Since 27=128<200<256=282^7 = 128 < 200 < 256 = 2^8, we have 7<log⁡2(200)<87 < \log_2(200) < 8

More precisely, log⁡2(200)≈7.64\log_2(200) \approx 7.64

Since we need integers, n+2≤7n+2 \leq 7, so n≤5n \leq 5

Therefore: −4≤n≤5-4 \leq n \leq 5

This means n∈{−4,−3,−2,−1,0,1,2,3,4,5}n \in \{-4, -3, -2, -1, 0, 1, 2, 3, 4, 5\}


We calculate 3+3n+13+3^{n+1} for each value of nn:

nnn+1n+13n+13^{n+1}3+3n+13+3^{n+1}Integer?
-4-3127\tfrac{1}{27}3+127=82273 + \tfrac{1}{27} = \tfrac{82}{27}No
-3-219\tfrac{1}{9}3+19=2893 + \tfrac{1}{9} = \tfrac{28}{9}No
-2-113\tfrac{1}{3}3+13=1033 + \tfrac{1}{3} = \tfrac{10}{3}No
-10113+1=43 + 1 = 4Yes
01333+3=63 + 3 = 6Yes
12993+9=123 + 9 = 12Yes
2327273+27=303 + 27 = 30Yes
3481813+81=843 + 81 = 84Yes
452432433+243=2463 + 243 = 246Yes
567297293+729=7323 + 729 = 732Yes

The integer values of 3+3n+13+3^{n+1} are: {4,6,12,30,84,246,732}\{4, 6, 12, 30, 84, 246, 732\}

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