Posted by **Dhanalakshmi** on Wednesday, March 16, 2011 at 8:58am.

In Geometric progression the sum of first of three terms is 28 and the product is 512 find those numbers

- math -
**bobpursley**, Wednesday, March 16, 2011 at 9:18am
a+ar+ar^2=28

a^3 * r^3=512

one the second equation, take the cube root of each side.

ar=cubrt(512)=8

a+8+ar^2=28

a(1+r^2)=20

but a= 8/r

8(1+r^2)=20r

8r^2-20 r+8=0

r=(20)+-sqrt(400-256) /16

r=20+- sqrt(144) /16 = (20+-12)/16=2 or 1/2

then a= 4 or 16

check a=4, r=2

4 + 8 + 16=28

a^3 r^3=64*8=512 checks, a=4, r=2

check a=8, r=1/2

8 +4 + 2 does not check.

## Answer this Question

## Related Questions

Math (Geometric Progression) - 5 distinct positive reals form an arithmetic ...

math - There are two positive numbers that can be inserted between 3 and 9 such ...

Math - 5 distinct positive reals form an arithmetic progression. The 1st, 2nd ...

math - 1)Find the sum of the first eight terms of the Geometric progression 256,...

Math - The product of three numbers in geometric progression is 1, their sum is...

Maths - 1..The first 2 terms of a geometric progression are the same as the ...

Arithmetic - The first, second and third terms of a geometric progression are 2k...

arithmetic - 1. The first and last term of an A.P are, a and l respectively, ...

arithmetic - 1. The first and last term of an A.P are, a and l respectively, ...

math - The first, the third and the seventh terms of an increasing arithmetic ...