Question

Stolen problem from Dinda :D
Without calculator, find 8^(-x)+8^x
if you are given that 4^x+4^(-x)=7

Answer 1

2^(2x)+2^(-2x)=7
(2^x+2^-x)^2=9
2^x+2^-x=3;
let a=2^x
a+1/a=3
(a+1/a)^3=27
a^3+1/a^3+3(a+1/a)=27
a^3+1/a^3=18
but a^3=8^x. so ans is 18

Answer 2

Awesome! :D

Answer 3

if u have any more prob. u can post it....i'll try

Answer 4

Ok, I'll repost my old problem that has no answer

Answer 5

ok

Answer 6

i have answered your next problem...