Bài 1:
a) 4sin23x + 2(\(\sqrt{3}\)+1) cos 3x - \(\sqrt{3}\)= 4
b) cos2x + 9cosx + 5 = 0
c) 4cos5(2 - 6x) + 16cos2(1 - 3x) =13
d)\(\frac{1}{cos^2x}-\left(3+\sqrt{3}\right)tanx-3+\sqrt{3}=0\)
e) \(\frac{3}{cosx}+tan^2x=9\)
f) 9 - 13cosx + \(\frac{4}{1+tan^2x}=0\)
g) \(\frac{1}{sin^2x}=cotx+3\)
h) \(\frac{1}{cos^2x}+3cot^2x=5\)
i) cos2x - 3cosx = 4cos2\(\frac{x}{2}\)
k) 2cos2x +...
Đọc tiếp
Bài 1:
a) 4sin23x + 2(\(\sqrt{3}\)+1) cos 3x - \(\sqrt{3}\)= 4
b) cos2x + 9cosx + 5 = 0
c) 4cos5(2 - 6x) + 16cos2(1 - 3x) =13
d)\(\frac{1}{cos^2x}-\left(3+\sqrt{3}\right)tanx-3+\sqrt{3}=0\)
e) \(\frac{3}{cosx}+tan^2x=9\)
f) 9 - 13cosx + \(\frac{4}{1+tan^2x}=0\)
g) \(\frac{1}{sin^2x}=cotx+3\)
h) \(\frac{1}{cos^2x}+3cot^2x=5\)
i) cos2x - 3cosx = 4cos2\(\frac{x}{2}\)
k) 2cos2x + tanx=\(\frac{4}{5}\)
10. ĐKXĐ: \(x\ne\frac{\pi}{2}+k\pi\)
\(2cos2x+tanx=\frac{4}{5}\)
\(\Leftrightarrow4cos^2x-2+tanx=\frac{4}{5}\)
\(\Leftrightarrow\frac{4}{1+tan^2x}+tanx-\frac{14}{5}=0\)
Đặt \(tanx=t\)
\(\Rightarrow\frac{20}{1+t^2}+5t-14=0\)
\(\Leftrightarrow5t^3-14t^2+5t+6=0\)
\(\Leftrightarrow\left(t-2\right)\left(5t^2-4t-3\right)=0\)
\(\Rightarrow\left[{}\begin{matrix}t=2\\t=\frac{2+\sqrt{19}}{5}\\t=\frac{2-\sqrt{19}}{5}\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}tanx=2=tana\\tanx=\frac{2+\sqrt{19}}{5}=tanb\\tanx=\frac{2-\sqrt{19}}{5}=tanc\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}x=a+k\pi\\x=b+k\pi\\x=c+k\pi\end{matrix}\right.\)
9.
\(\Leftrightarrow cos2x-3cosx=2\left(cosx+1\right)\)
\(\Leftrightarrow2cos^2x-1-3cosx=2cosx+2\)
\(\Leftrightarrow2cos^2x-5cosx-3=0\)
\(\Rightarrow\left[{}\begin{matrix}cosx=3\left(l\right)\\cosx=-\frac{1}{2}\end{matrix}\right.\)
\(\Rightarrow x=\pm\frac{2\pi}{3}+k2\pi\)