Find the first term of the arithmetic sequence in a27=-1/2 and the common difference is 2

1) First term = -105/2

2) The first option is the correct answer 9/2[ 2 + 26]

Step-by-step explanation:

It is given that,

The first term of the arithmetic sequence in which a27=-1/2

and the common difference is 2  

To find the First term

First term of an AP be a and common difference d the nth term can be written as,

an = a + (n-1)d

Here n = 27

d = 2 , a27 = -1/2

a + (26 x 2) = -1/2

a = -105/2

From the figure We get  an = 3n - 1

To find first term a1 and ninth term s9  

a1 = 3 x 1 - 1 = 2

a9 = 3x 9  - 1 = 26

Sum of nth term of an AP  

n/2[first term  + Last term]

first term a1 and Last term = 26

Sum of first 9 terms S9

S9 = 9/2[ 2 + 26]

First option is the correct answer

according to the triangle sum theorem, all the angles in a triangle must add up to 180 degrees. if we know one angle is already 90, we do 180-90=90. the other 2 angles must add up to 90, exactly.

step-by-step explanation: