Câu 23: Trang 84 - sgk toán 9 tập 1
Tính :
a. $\frac{\sin 25^{\circ}}{\cos 65^{\circ}}$
b. $\tan 58^{\circ}-\cot 32^{\circ}$
Bài Làm:
Ta có :
a. $\frac{\sin 25^{\circ}}{\cos 65^{\circ}}$
= $\frac{\sin (90^{\circ}-25^{\circ})}{\cos 65^{\circ}}$
= $\frac{\cos 65^{\circ}}{\cos 65^{\circ}}=1$
Vậy $\frac{\sin 25^{\circ}}{\cos 65^{\circ}}$= 1 .
b. $\tan 58^{\circ}-\cot 32^{\circ}$
= $\tan (90^{\circ}-58^{\circ})-\cot 32^{\circ}$
= $\cot 32^{\circ}-\cot 32^{\circ}=0$
Vậy $\tan 58^{\circ}-\cot 32^{\circ}$ = 0 .