Friday, August 29, 2014

`a_4 = 16, a_10 = 46` Write the first 5 terms of the arithmetic sequence.

`a_4=16 `  


`a_10=46`


To determine the first five terms of this arithmetic sequence, consider its nth term formula which is:


`a_n=a_1+(n-1)d`


To apply this, plug-in the given nth terms.


Plugging in a_4=16, the formula becomes:


`16=a_1 + (4-1)d`


`16=a_1+3d `          (Let this be EQ1.)


Also, substituting a_10=46, the formula becomes:


`46=a_1+(10-1)d`


`46=a_1+9d `          (Let this be EQ2.)


Then, use these two equations to solve for the...

`a_4=16 `  


`a_10=46`


To determine the first five terms of this arithmetic sequence, consider its nth term formula which is:


`a_n=a_1+(n-1)d`


To apply this, plug-in the given nth terms.


Plugging in a_4=16, the formula becomes:


`16=a_1 + (4-1)d`


`16=a_1+3d `          (Let this be EQ1.)


Also, substituting a_10=46, the formula becomes:


`46=a_1+(10-1)d`


`46=a_1+9d `          (Let this be EQ2.)


Then, use these two equations to solve for the values of a_1 and d. To do so, isolate a_1 in the first equation.


`16=a_1+3d`


`16-3d=a_1`


Plug-in this to the second equation.


`46=a_1+9d`


`46=16-3d+9d`


`46=16+6d`


`30=6d`


`5=d`


Then, solve for a_1. To do so, plug-in d=5 to the first equation.


`16=a_1 + 3d`


`16=a_1+3(5)`


`16=a_1+15`


`1=a_1`


Then, plug-in these two values a_1=1 and d=5 to the formula of nth terms of arithmetic sequence.


`a_n=a_1+(n-1)d`


`a_n=1+(n-1)(5)`


`a_n=1+5n-5`


`a_n=5n-4`


Now that the formula of a_n is known,  use this to solve for the values of a_2, a_3 and a_5.  (Take note that the values of a_1 and a_4 are already known.)


1st term: `a_1=1`


2nd term: `a_2=5(2)-4=6`


3rd term: `a_3=5(3)-4=11`


4th term: `a_4=16`


5th term: `a_5=5(5)-4=21`


Therefore, the first five terms of the arithmetic sequence are {1, 6, 11, 16, 21,...}.

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