Question

Answer 1

1: 90<a<180

=>cosa<0

=>\(cosa=-\sqrt{1-\left(\dfrac{1}{3}\right)^2}=-\sqrt{\dfrac{8}{9}}=-\dfrac{2\sqrt{2}}{3}\)

tan a=sin a/cosa

\(=\dfrac{1}{3}:\dfrac{-2\sqrt{2}}{3}=-\dfrac{1}{2\sqrt{2}}\)

2:

\(sina=\sqrt{1-\dfrac{4}{9}}=\dfrac{\sqrt{5}}{3}\)

\(cota=\dfrac{-2}{3}:\dfrac{\sqrt{5}}{3}=-\dfrac{2}{\sqrt{5}}\)

4: 0<a<90

=>sin a>0

=>\(sina=\sqrt{1-\dfrac{9}{16}}=\dfrac{\sqrt{7}}{4}\)

\(A=\dfrac{tana+3cota}{tana+cota}\)

\(=\dfrac{\dfrac{\sqrt{7}}{3}+3\cdot\dfrac{3}{\sqrt{7}}}{\dfrac{\sqrt{7}}{3}+\dfrac{3}{\sqrt{7}}}=\dfrac{17}{8}\)

1A

2C

3A

4: Đề sai rồi bạn

5B

6D