Question

If the square of the 7th term of an arithmetic progression with positive common difference equals the product of the 3rd and 17th terms, then the ratio of the first term to the common difference is

• A. 2 : 3
• B. 3 : 2
• C. 3 : 4
• D. 4 : 3

Answer 1

The correct option is A

2 : 3

Let the first term be a and the common difference d.

Given, $(a+6d{)}^2=(a+2d\left)\right(a+16d)a^2+36d^2+12ad=a^2+32d^2+18ad4d=6a\frac{a}{d}=\frac{2}{3}.$