If each term of a geometric progression (GP) is positive and is the sum of two preceding terms, then the common ratio of the GP is: |
$\frac{\sqrt{5}-1}{2}$ $\frac{1-\sqrt{5}}{2}$ $\frac{\sqrt{5}+1}{2}$ $\frac{\sqrt{3}+1}{2}$ |
$\frac{\sqrt{5}+1}{2}$ |
The correct answer is Option (3) → $\frac{\sqrt{5}+1}{2}$ Step 1: Let the GP be $a, ar, ar^2, ar^3, \dots$ The property given: $\text{Each term is the sum of the two preceding terms: } ar^n = ar^{n-1} + ar^{n-2}, \ n \ge 2$ Divide both sides by $ar^{n-2}$ (positive, non-zero): $r^2 = r + 1$ Step 2: Solve quadratic equation $r^2 - r - 1 = 0$ $r = \frac{1 \pm \sqrt{1 + 4}}{2} = \frac{1 \pm \sqrt{5}}{2}$ Since all terms are positive, we take the positive root: $r = \frac{1 + \sqrt{5}}{2}$ |