Sử dụng định nghĩa các tỉ số lượng giác của một góc nhọn để chứng minh rằng. Với góc nhọn α tùy ý, ta có:

$tg\alpha =\frac{\sin \alpha }{\cos \alpha },cot\alpha =\frac{\cos \alpha }{\sin \alpha },ta\alpha .cotg\alpha =1$

Gợi ý: Sử dụng định lí Pitago.

Choose the best answer.

I think you should buy _____  pack of mineral water instead. And you can also buy _____  snacks such as potato crisps, 3 kilos of mandarins, 2 kilos of apples, 3 bunches of bananas, ______  cookies and soft candies.

Choose the best answer.

We should decorate our living room with _____ orange banner. We also need ________  ribbons, balloons, party hats and costume.

Choose the best answer.

I think that ______ cauliflower is not enough for 3 people. Let’s buy one more.