In an ascending geometric sequence, (𝑎5)2=3𝑎10, and for any three consecutive terms, 2(𝑎𝑛+𝑎𝑛+2)=5𝑎𝑛+1. Find the first term of the geometric sequence.
Question
In an ascending geometric sequence,
and for any three consecutive terms,
Find the first term of the geometric sequence.
Solution
To solve this problem, we need to use the properties of geometric sequences and the given equations.
-
In a geometric sequence, each term is the product of the previous term and a constant ratio (r). So, we can express the 5th term (a5) and the 10th term (a10) in terms of the first term (a1) and the ratio (r) as follows: a5 = a1 * r^4 and a10 = a1 * r^9.
-
Substitute these expressions into the first given equation (a5)^2 = 3a10, we get: (a1 * r^4)^2 = 3 * a1 * r^9. Simplify this equation, we get: a1^2 * r^8 = 3 * a1 * r^9. Divide both sides by a1 * r^8, we get: a1 = 3/r.
-
For the second given equation, we know that for any three consecutive terms in a geometric sequence, the middle term is the geometric mean of the other two. So, we can express the equation 2(a_n + a_n+2) = 5a_n+1 as 2(a1 * r^(n-1) + a1 * r^(n+1)) = 5 * a1 * r^n. Simplify this equation, we get: 2(r - r^3) = 5r^2. Divide both sides by 2r, we get: 1 - r^2 = 5/2 * r. This is a quadratic equation in terms of r.
-
Solve this quadratic equation, we get two possible values for r: r = 1/2 or r = -5.
-
Substitute these values into the equation a1 = 3/r, we get two possible values for a1: a1 = 6 or a1 = -3/5.
-
However, since the sequence is ascending, the ratio must be greater than 1. So, the valid solution is a1 = -3/5 and r = -5.
So, the first term of the geometric sequence is -3/5.
Similar Questions
In an ascending geometric sequence, (𝑎5)2=3𝑎10, and for any three consecutive terms, 2(𝑎𝑛+𝑎𝑛+2)=5𝑎𝑛+1. Find the first term of the geometric sequence.
The first five terms of a number sequence are shown below.10,14,18,22,26Find an expression for the (𝑛+1)th term, in terms of 𝑛.
Find the 12th term of the geometric sequence 2, comma, minus, 8, comma, 32, comma, point, point, .2,−8,32,...
Find a formula for the nth term of the geometric sequence. Then find the indicated nth term of the geometric sequence.15th term: 4, 8, 16,. . .
The sequence below is the start of the triangular number sequence.Work out the next two number terms in the sequence.
Upgrade your grade with Knowee
Get personalized homework help. Review tough concepts in more detail, or go deeper into your topic by exploring other relevant questions.