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**shibble** Assume that R2>R2 is a linear transformation such that

T|1| =|1|

|2| |-3|

and

T|3| =|2|

|-1| |1|

Find the standard matrix of T.

Ok, so I get that |1,2|=e1+2e2 and that |3,-1|=3e1-e2, but what do I do from there on? It shows in the solutions that

e1=1/7|1,2| + 2/7|3, -1|

e2=3/7|1,2|-1/7|3,-1|

I understand that the are using the same thing from e1+2e2 and 3e1-e2, but where is the divisor of 7 coming from?

Sorry if it's formatted badly, I can scan the original page? Thanks