Câu hỏi:

a² = b² + c² – 3bc;

a² = b² + c² + bc;

a² = b² + c² + 3bc;

a² = b² + c² – bc

1;

0;

C. – 1;

Không xác định

\(\sqrt {43} \);

\(2\sqrt {13} \);

8;

\(8\sqrt 3 \)

tan(α) > 0; cot(α) > 0;

tan(α) < 0; cot(α) < 0;

tan(α) > 0; cot(α) < 0;

tan(α) < 0; cot(α) > 0

sin(180° – α) = – cos α;

sin(180° – α) = sin α;

sin(180° – α) = cos α

\[\cot \alpha = \frac{4}{3}\];

\[\sin \alpha = \frac{3}{5}\];

\[\tan \alpha = \frac{4}{5}\]

\[\sin \alpha = - \frac{3}{5}\]

sin(α) > 0; cos(α) > 0;

sin(α) > 0; cos(α) < 0;

sin(α) < 0; cos(α) > 0;

sin(α) < 0; cos(α) < 0

1;

– 1;

0;

Không xác định

5;

\(\frac{5}{3}\);

7;

7;

D.\(\frac{7}{3}\)

\(\cos 750^\circ = \frac{{\sqrt 3 }}{2}\);

\(\sin 1320^\circ = - \frac{{\sqrt 3 }}{2}\);

\(\cot 1200^\circ = \frac{{\sqrt 3 }}{3}\);

\(\tan 690^\circ = - \frac{{\sqrt 3 }}{3}\)