Theory question 106
ProgressionsThe third term of a Geometric Progression (G.P) is 360 and the sixth term is 1215. Find the first four terms.
Show the model answer
Model answer
ar2 = 360 and ar5 = 1215. Divide: r3 = 1215/360 = 27/8, so r = 3/2.
a = 360 ÷ (3/2)2 = 360 × 4/9 = 160.
First four terms: 160, 240, 360, 540.
Explanation
Dividing the two term equations removes a and leaves r³.