Detect dependence and use a basis

Problem

In R3\mathbb R^3, let v1=(1,0,1)v_1=(1,0,1), v2=(0,1,1)v_2=(0,1,1), and v3=(1,1,2)v_3=(1,1,2). Determine whether the three vectors are independent. Give a basis and dimension for their span, then give the coordinates of x=(2,3,5)x=(2,3,5) in your basis.

Reveal answer or reference solution

Since v3=v1+v2v_3=v_1+v_2, the three-vector list is dependent. The vectors v1,v2v_1,v_2 are independent, so B=(v1,v2)B=(v_1,v_2) is a basis and the span has dimension 22. Because x=2v1+3v2x=2v_1+3v_2, its BB-coordinates are [x]B=(2,3)T[x]_B=(2,3)^{\mathsf T}. The basis matrix PB=[v1 v2]P_B=[v_1\ v_2] performs the change to standard coordinates: x=PB[x]Bx=P_B[x]_B.

Outcome

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