# intro cal

posted by
**Emma** on
.

the first 3 term of a geometric progression are

k-4, 2k-4, 4k+4.

what is the value of k?

can someone help please!

in any geometric progression any term divided by its previous term gives you the common ratio, so ....

(2k-4)/(k-4) = (4k+4)/(2k-4)

cross-multiply and proceed.

I comes out nice, the square term cancels.

how do i cross multiply this?i get confused easiy when doing cross multiply in division...

(2k-4)(2k-4) = (k-4)(4k+4)

4k^2 - 16k + 16 = 4k^2 - 12k - 16

-4k = -32

k=8

ooh so you times it by the opposite!silly me...

Thank you soo much!!

yes, in general

a/b = c/d -----> bc = ad

try it with equivalent fractions

we know 2/3 = 10/15

then 2*15 = 3*10 ...true!