Question

Find 3 numbers in G.P whose sum is 28 and whose product is 512

Answer 1

4, 8 and 16

Explanation:

a/r ×a×ar =512

a^3 =512

a = cube root of 512

a=8

8/r+8+8r=28

8r^2+8=20r

8r^2-20r+8=0

8r^2-16r-4r+8=0

8r(r-2)-4(r-2)=0

(8r-4)(r-2)=0

r=2

8r=4

so r=2 or r=1/2

so of r is 2

8/2=4

and 8×2=16