The angle of 1 ' (minute of arc) in radian is nearly equal to

First, convert one minute to a second, $1^{\text{'}}=\left(\frac{1}{60}\right)°$ and then convert it into radian, $\frac{1}{60}\times \frac{\pi }{180} \mathrm{rad}$, so we can say that in one minute there is, $2.91\times {10}^{-4} \mathrm{rad}$.