Question

Ét o ét giúp mik câu vd 3 va ạ

Answer 1

a: 3/2pi<=a<=2pi

=>sin a<0

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

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

\(sin2a=2\cdot sina\cdot cosa=2\cdot\dfrac{-\sqrt{5}}{3}\cdot\dfrac{2}{3}=\dfrac{-4\sqrt{5}}{9}\)

b: \(A=\dfrac{9\cdot\dfrac{5}{9}+\sqrt{5}\cdot\dfrac{-\sqrt{5}}{2}}{5+6\cdot\dfrac{2}{3}}=\dfrac{5}{18}\)

d: sin(a+pi/4)

=1/căn 2(sina+cosa)

\(=\dfrac{1}{\sqrt{2}}\cdot\dfrac{-\sqrt{5}+2}{3}=\dfrac{-\sqrt{5}+2}{3\sqrt{2}}\)