The second and fourth term of a geometric series is 100 and 225 respectively. Find the common ratio and first term of the series. Round your answer to 2 d.p if necessary

Formula for a Geometric series for term n = arn , where a = the first term and r = common ratio.Therefore, with the information given we can write that ar2 = 100 and ar4 = 225 , where a and r are the constants we're trying to find
By dividing these two equations together we get that ar4 / ar2 = 225 / 100this can then be simplified to r2 = 2.25, which can be square rooted to show that r = 1.5
After working this out, when can sub r=1.5 back into one of the equations for the two terms given, for example ar2 = 100, to get that a(1.5)2 = 100 by dividing by 1.52 on both sides we can show that a = 44.44 to 2 d.p

Related Maths A Level answers

All answers ▸

The curve C has equation x^2 – 3xy – 4y^2 + 64 = 0; find dy/dx in terms of x and y, and thus find the coordinates of the points on C where dy/dx = 0


Integrate 2x^2 + 4


A line L is parallel to y=4x+5 and passes through the point (-1, 6). Find the equation of the line L in the form y=ax+b . Find also the coordinates of its intersections with the axes.


Find the constant term in the expression (x^2-1/x)^9