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Oksana_A [137]
3 years ago
8

If the fifth and eighth terms of an arithmetic sequence are minus 9 and minus 21, respectively, what are the first four terms of

the sequence?
Mathematics
1 answer:
Reil [10]3 years ago
4 0
One way to do this problem is to determine the common difference.  If the 5th and 8th terms are -9 and -21, we can do this by subtracting -9 from -21:

-21-(-9) = -12.  The 5th and 8th terms are not consecutive, so we have to think in terms of (8-5), or 3, times the common difference to get from -9 to -21.

Note that -12 divided by 3 is -4.  Thus, the common difference is -4.

Check:  -9 - 4 = -13; -13 - 4 = -17; -17 - 4 = -21 (which is correct).

We know that the 5th term is -9.  To find the 4th term, work backwards:  subtract (-4) from -9, which produces -9+4=-5.

The fourth term is -5.  Subtracting -4 from this (which is the same as adding 4 to this -5) produces the third term; it is -1.  Can you now find the 2nd and 1st terms using the same approach?

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Answer:

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Step-by-step explanation:

Given:

45x^3a+27xa^2= 9xa

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45x^3a+27xa^2= 9xa(5x^2+3a)

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Three vertices of parallelogram ABCD are A(2,-6),B(-1,2),C(5,3).find the coordinates of vertex D
salantis [7]

Check the first picture below.


for a parallelogram, it has to have two pairs of parallel sides, so BC || AD and AB || CD.

if two lines are parallel, they have the same slope, namely the <u>same rise and run</u>.

notice, the line BC has a run of 6 and a rise of 1, <u>arrows in red</u>, therefore, AD must also have a run of 6 and a rise of 1, so if we move from A 6 units over and 1 up, we'd end up at point D.


now, for part atop

Check the 2nd picture, in a parallelogram, opposite sides are parallel and opposite angles are equal, so if WLP is 144°, then PNW is also 144°.

in a parallelogram, diagonals bisect each other, so each cut the other in halves, so if PM is 9 then MW is also 9 and thus PW is just 9+9=18.


now, about QRST.

notice what we said about a parallelogram above, thus


\bf 8x+13=11x-23\implies 8x+36=11x\implies 36=3x \\\\\\ \cfrac{36}{3}=x\implies \boxed{12=x} \\\\[-0.35em] ~\dotfill\\\\ 2y+12=4y-4\implies 2y+16=4y\implies 16=2y \\\\\\ \cfrac{16}{2}=y\implies \boxed{8=y}


so then TQ ==> 2(8) + 12 ==> 16 + 12 ==> 28.

∡Q ==> 8(12) + 13 ==> 96 + 13 ==> 109°.

and since in a parallelogram, adjacent interior angles add up to 180°, then ∡Q + ∡T = 180°.

∡T ==> 180 - 109 ==> 71°.

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