Công thức :
$\Delta D=\left( {{n}_{t}}-{{n}_{d}} \right)A$
……………………..
Câu 81:
$\Delta D=\left( {{n}_{t}}-{{n}_{d}} \right)A$
$0,141=\left( {{n}_{t}}-1,5145 \right).6$
$\to {{n}_{t}}=1,538$
$\to $ câu $A$
…………………………
Câu 82:
$\Delta D=\left( {{n}_{t}}-{{n}_{d}} \right)A$
$\Delta D=\left( 1,6852-1,6442 \right).0,1$
$\Delta D=0,0041\,\,\left( rad \right)$
$\to $ câu $B$