1.

If `(5z_1)/(7z_2)` is purely imaginary then `|(2z_1+3z_2)/(2z_1-3z_2)|=`

Answer» `z_1=r_1e^(itheta_1)`
`z_2=r_1e^(itheta_2)`
`5z_1/7z_2->(5r_1e^(itheta_1))/(7r_2e^(itheta_2)`
`theta_1-theta_2=2npipmpi/2`
`|(2z_1+3z_2)/(2z_1-3z_2)|`
`|(1+3/2z_2/z_1)/(1-3/2z_2/z_1)|`
`|(1+3/2x i)/(1-3/2x i)|`
`sqrt(1^2+(3/2x)^2)/sqrt(1^2+(-3/2x)^2)`
`1`


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