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 #2
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Mar 24, 2024
 #1
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Analyzing the function f(x) = floor((2 - 3x) / (x + 3)):

 

The denominator (x + 3) is 0 when x = -3. This means f(x) is undefined at x = -3.

 

We will need to consider different cases based on the sign of the denominator (x + 3) and the relative values of 2 - 3x compared to 0.

 

Cases for f(x):

 

x < -3: In this case, both denominator (x + 3) and numerator (2 - 3x) are negative. Dividing two negative numbers results in a positive value.

 

Since we take the floor (greatest integer less than or equal to), f(x) will be -1.

 

-3 < x < 2/3: Here, the denominator (x + 3) is positive, but the numerator (2 - 3x) is negative.

 

Dividing a positive by a negative results in a negative number.

 

Taking the floor of a negative number keeps it negative, so f(x) will be -2.

 

x = 2/3: At this specific point, the numerator becomes 0, and the result of the division is 0. The floor of 0 is 0, so f(x) = 0.

 

x > 2/3: In this case, both the numerator (2 - 3x) and denominator (x + 3) are positive. Dividing two positive numbers results in a positive value.

 

Taking the floor doesn't change the positive sign, so f(x) will be 1.

 

Evaluating the sum:

 

The key to evaluating the sum efficiently is to recognize that for a large range of x values (between -3 and 2/3), f(x) will be -2.

 

We can exploit this by calculating the number of terms that fall into this range and summing the contributions from the remaining terms separately.

 

Number of terms where f(x) = -2:

 

We know x = -3 falls outside this range (f(x) is undefined).

 

The range ends when x = 2/3, which is between terms 1000 and 1001 (1000th term is x = 999 and 1001st term is x = 1000).

 

Therefore, there are 1000 - (-3) + 1 = 1004 terms where f(x) = -2.

 

Contribution from terms where f(x) = -2:

 

Each term contributes -2 to the sum.

 

Total contribution = -2 * (number of terms) = -2 * 1004 = -2008

 

Remaining terms:

 

We need to consider terms for x < -3 (f(x) = -1), x = 2/3 (f(x) = 0), and x > 2/3 (f(x) = 1).

 

There are very few terms less than -3 (all negative x values), and they can be ignored for a large sum like this (their contribution will be negligible).

 

There's only one term for x = 2/3, contributing f(2/3) = 0.

 

The remaining terms from x slightly greater than 2/3 to x = 1000 will all have f(x) = 1. The exact number of these terms depends on the specific values, but there will be significantly fewer compared to the 1004 terms with f(x) = -2.

 

Overall Sum:

 

Sum from terms with f(x) = -2: -2008

 

Contribution from f(2/3) (x = 2/3): 0

 

Contribution from remaining terms with f(x) = 1 (positive but less than those with -2): + (positive value)

 

Since the number of terms with f(x) = 1 is significantly less than those with -2, and there's a negligible contribution from terms less than -3, the positive value from the remaining terms will be much smaller than 2008.

 

Therefore, the overall sum f(1) + f(2) + ... + f(999) + f(1000) is equal to -2008.

Mar 24, 2024
Mar 23, 2024

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