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## Homework Statement

The Star Alpha Centauri is 4.0 light years away. At what constant speed must a spacecraft travel from earth if it is to reach the star in 3.0 years, as measured by the travelers on the spacecraft.

## Homework Equations

Length Contraction:

L = Lo*(sqrt(1-(u

^{2}/c

^{2}))) , Lo = Length proper

Time Dilation:

T = To / (sqrt(1-(u

^{2}/c

^{2}))) ,To = Time proper

## The Attempt at a Solution

Because I'm new to the topic I can only use the formulas for basic length contractions and time dilation. But I am unsure how to use them together. Any help + explanation will be greatly appreciated.