Math

posted by .

Find a1 in a geometric series for which Sn=189,r=1/2,and an=3.

Sn=a1(1-r^n)/1-r
189=a1(1-1/2^3)/1-1/2
189=a1(-.5)/.5
189/-.25
a1=-756

  • Math -

    YOur third line is wrong

    should be:

    189 = a(1 - 1/8)/(1 - 1/2)
    189 = a(7/8)/(1/2)
    189 = a(7/4)
    756 = 7a
    108 = a

    (check 108+54+27 = 189 !)

Respond to this Question

First Name
School Subject
Your Answer

Similar Questions

  1. math. HOW DO I CONVERT A DECIMAL TO A FRACTION

    how do i convert a decimal to fraction in SIMPLEST FORM?
  2. chemistry

    Temp - 650 Pressure - 760mm Hg mass - 0.927g volume - ?
  3. chem

    Consider a Carnot engine operating between the temperatures of 300. K and 189 K. Find the efficiency of this engine. Assume, now, that the isothermal step at 300. K is not reversible and the expansion takes place against a constant …
  4. Geometry repost

    "yes, except 20/36 / 21/x x= 189/5 = 37.8 seems to have a typo, no original equation" There was a typo, it should have been: 20/36 = 21/x x= 189/5 = 37.8 So is this correct?
  5. MATH

    1.32 + 0.987 + 3.07 = a-4.089 b-5.089 c-5.189 d-6.189 e-13.972 answer-5.089
  6. college physics

    A 0.384 kg puck, initially at rest on a horizon- tal, frictionless surface, is struck by a 0.189 kg puck moving initially along the x axis with a speed of 2.7 m/s. After the collision, the 0.189 kg puck has a speed of 1.7 m/s at an …
  7. Algebra 2

    5+(-5/2)+(5/4) Sn=189 Find n for the given sum if the geometric series
  8. Math

    Whars 189.80. Times 6.25% less 33 1/3 % Is it 189.80 + 11.86 = 201.66 - 67.22 = $134..44
  9. Chemistry

    A chemist wants to make 150 mL of a 1.26 M solution of carbonic acid to be used in the lab. How many grams of H2CO3 does the chemist need to make this solution?
  10. Math

    You shop for bikes and find 7 types priced at 119 139 149 179 189 199 and 209. you want to buy the 189 bike would you use the mean median and mode to convince your parents that this is a reasonable price for a bike?

More Similar Questions