Linear Algebra: Basis

[phyxius117]

Homework Statement

Homework Equations

The Attempt at a Solution

I don't know how to do this problem.. Help please!

 

[silvermane]

Here, maybe this will help you understand projections onto a subspace:
http://www.cliffsnotes.com/study_guide/Projection-onto-a-Subspace.topicArticleId-20807,articleId-20792.html [Broken]

Do you understand the concept of orthogonality?