You can put this solution on YOUR website! Find a vector that has the same direction as 3i - 7j and twice the magnitude.
The direction is tan^-1(-7/3) in the 4th quadrant.
It is -66.8 degrees or +293.199 degrees
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The magnitude of the given number is sqrt(7^2+3^2)=sqrt58 =7.616
Twice that magnitude = 15.23
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The vector is 15.23(cos293.199 + isin293.199)
or
6 - 14i
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Cheers,
Stan H.