1.

If `z = (3+ 7i) (a +ib)` where a,`b in in Z- {0}`, is purely imaginary , then the minimum value of `|z|` isA. 74B. 45C. 58D. 65

Answer» Correct Answer - C
`z=(3a-7b)+i(3b+7a)`
For z to be purely imaginary, we have
`3a=7b`
`rArra =7 or b=3` (for least value of `|z|`)
`rArr |z| =|3+7i|`


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