Melody

That is much better MathsGod1     

$$\\1000=X(1+0.055)^{10}\\\\
1000\div (1.055)^{10}=X\\\\$$

inverse cos is the same as arc cos

so press [2nd]  [acos]  then your number

I don't think that you have given enough information :/

Well

$$\\5^3=125\\
so\\
257=5^3+5^3+1^3+1^3+1^3+1^3+1^3+1^3+1^3\\$$

Maybe there is a way to get 257 by adding less cubes   

Edited

Answer:

what is it that you want to do with fraction?

Here is a starter page

$$cos(2x) \\
= cos^2x-sin^2x\\
=1-sin^2x-sin^2x\\
=1-2sin^2x$$

Congratulations KimLee,

I am very glad we could help 

I have added this to the logic puzzles thread  :)