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Oct 25, 2023
 #1
avatar+2 
+1

Assuming that you are referring to the sum of the infinite sequence of a,

 

Let's try to expand the terms

\(\begin{align} a_1 &=( \frac{1}{2}) \\\\ a_2 &= \frac{1}{6} = \frac{3}{6}-\frac{2}{6} \\ &=( \frac{1}{2}) -( \frac{1}{3})\\\\ a_3 &= \frac{1}{12} = \frac{4}{12}-\frac{3}{12} \\ &=( \frac{1}{3}) -( \frac{1}{4}) \\\text{and so on...} \end{align}\)


Hence, we can conclude that every term of an (apart from a1equals to \(\frac {1}{n} - \frac {1}{n+1} \)

Therefore, the sum of such an infinite sequence is presented as ...\(a_1 + a_2 + a_3 + \ldots =\frac{1}{2} + \left(\frac{1}{2} - \frac{1}{3}\right) + \left(\frac{1}{3} - \frac{1}{4}\right) + \left(\frac{1}{4} - \frac{1}{5}\right) + \ldots +\left(\frac{1}{n-2} - \frac{1}{n-1}\right) + \left(\frac{1}{n-1} - \frac{1}{n}\right))\)

... where n in this case would be infinity,

equals to...

\(a_1 + a_2 + a_3 + \ldots =\frac{1}{2} + \frac{1}{2} - \frac{1}{n} = 1 - \frac{1}{n}\)

 

the sum of the sequence approaches 1 

further explanation (to the best of my abilities below)

.

.

.

.

 

As you can imagine, even though \(\frac {1}{n} \) never reaches 0 but continues to decrease in value,

there is a point where the value of \(\frac {1}{n} \) would be so small

 

(think that when n = one trillion, \(\frac {1}{n} \) would result in 0.000000000001

1 - 0.000000000001 = 0.99999999999 

 - and n, as infinity, would not stop at one trillion,

meaning that as the sequence goes on, smaller and smaller values of  \(\frac {1}{n} \) would be subtracted from 1, )

 

 

Hence, we completely ignore the value of n, instead we can just say that 

the sum of the sequence approaches 1 

Oct 25, 2023
 #1
avatar+2 
0

Here are the solutions to the four geometry problems:

1. Since \angle PAQ = 13^\circ and \overline{AP} is an altitude of the triangle, we have \angle PBA = 90^\circ - 13^\circ = 77^\circ. Also, since \angle B > \angle C, we have \angle BAC > \angle BAC. Therefore, \angle RAC = 90^\circ - \angle BAC < 90^\circ - 77^\circ = 13^\circ.

2. Since M, N, and P are the midpoints of sides \overline{TU}, \overline{US}, and \overline{ST} of triangle STU, respectively, we have \overline{MP} = \overline{PN} = \overline{NM}. Also, since \overline{UZ} is an altitude of the triangle, we have \angle NZM = \angle NPM.

Therefore, \angle NZM + \angle NPM = 2 \angle NZM = 2 \angle UZN = 2(90^\circ - 73^\circ) = 34^\circ.

3. Since M, N, and O are the midpoints of sides \overline{KL}, \overline{LJ}, and \overline{JK}, respectively, of triangle JKL, we have \overline{MO} = \overline{ON} = \overline{NP} = \overline{PQ} = \overline{QR}. Also, since P, Q, and R are the midpoints of \overline{NO}, \overline{OM}, and \overline{MN}, respectively, we have \overline{PQ} = \overline{QR} = 2 \overline{PR}.

Therefore, the area of triangle PQR is:

[PQR] = 1/2 * PQ * QR = 1/2 * 2PR * 2PR = 2PR^2
Since the area of triangle PQR is 27, we have:

2PR^2 = 27
PR = \sqrt{27/2} = 3\sqrt{3/2}
Therefore, the area of triangle LPQ is:

[LPQ] = 1/2 * LP * PQ = 1/2 * (2PR) * 2PR = 2PR^2 = 2(3\sqrt{3/2})^2 = 54\sqrt{3}
4. Since D is the midpoint of median \overline{AM} of triangle ABC, we have \overline{MD} = \overline{DA}. Also, since E is the midpoint of \overline{AB}, we have \overline{AE} = \overline{EB}.

Therefore, triangle DMT is congruent to triangle AEB. Since the area of triangle ABC is 180, the area of triangle AEB is 90. Therefore, the area of triangle DMT is also 90.

Summary:

\angle RAC = 13^\circ
\angle NZM + \angle NPM = 34^\circ
[LPQ] = 54\sqrt{3}
[DMT] = 90

Oct 25, 2023
Oct 24, 2023

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