# mathematics

1}
the first term of an AP is 2 and the common difference is 3.Find the sum of the first 11 terms. 2}The 2nd and 5th terms of a GP are -6 and 48 respectively.Find the sum of the first four terms

1. 👍
2. 👎
3. 👁
1. using our basic formulas
S(11) = (11/2)(4 + 10(3))
= 187

t2 = ar = -6
t5 = ar^4 = 48
divide them:
r^3 = 48/-6 = -8
r = -2

in ar = -6
a = 3

sum(4) = a(r^4 - 1)/(r-1)
= 3((-2)^4 - 1)/(-2-1)
= 3(15)/-3
= -15

check:
first 4 terms are:
3 , -6, 12, -24

1. 👍
2. 👎
2. 15

1. 👍
2. 👎

## Similar Questions

1. ### maths

The 6th term of an A.P is twice the third and the first term is 3. Find the common difference and the 10th term and find the sum of the 1st 10 terms

2. ### arithmetic

the sum of the n termsof an ap whose first term is 5 and common difference is 36 is equal to the sum of 2n terms of another AP whose first term is 36 ans common difference is 5. Find n?

3. ### maths

The 12th term of exceeds the 3rd term by 36 of an a.p If it's 16th term is 64 find first term and common difference

4. ### Utech

The 6th term of an A.P is twice the third and the first term is 3. Find the common difference and the 10th term.

1. ### Math

The first term and last term of an arithmetic progression are -4 and 145 respectively. If the common difference is 4. (a) find the 12th term (b) find the 25th term.

2. ### Arithmetic Progression

In an AP the 6th term is half the 4th term and the 3rd term is 15. a. Find the fist term and the common difference. b. How many times are needed to give a sum that is less than 65?

3. ### Utech

The 9th term of an Arithmetic Progression is 8 and the 4th term is 20. Find the first term and the common difference.

4. ### Math

The 9th term of an arithmetic progression is three times the 5th term, find the relationship between the first term and common difference

1. ### maths

the 1st term of an ap is twice the common difference find in terms of the 5th term of the ap

2. ### Arithmetic Sequence

Given the third term of an arithmetic sequence less than the fourth term by three. The seventh term is two times the fifth term. Find the common difference and the first term.

3. ### math

The first term of an A.P is equal one-half of the common difference,d, find the 8th term of the A.P in the tern of 'd'

4. ### Math

the first term of a linear sequence is 3 and 8th term is 31 .find the common difference and hence find the 20th term