\(VT=\frac{cos2a.tan2a}{cos2a\left(tan4a-tan2a\right)}=\frac{sin2a}{\frac{cos2a.sin4a}{cos4a}-sin2a}=\frac{cos4a.sin2a}{sin4a.cos2a-sin2a.cos4a}\)
\(=\frac{cos4a.sin2a}{sin\left(4a-2a\right)}=\frac{cos4a.sin2a}{sin2a}=cos4a\)
\(VT=\frac{cos2a.tan2a}{cos2a\left(tan4a-tan2a\right)}=\frac{sin2a}{\frac{cos2a.sin4a}{cos4a}-sin2a}=\frac{cos4a.sin2a}{sin4a.cos2a-sin2a.cos4a}\)
\(=\frac{cos4a.sin2a}{sin\left(4a-2a\right)}=\frac{cos4a.sin2a}{sin2a}=cos4a\)
Chứng minh
\(\frac{1+cosx+cos2x+cos3x}{2cos^2x+cosx-1}\)=2cosx
\(\frac{cos4a\cdot tan2a-sin4a}{cos4a\cdot cot2a+sin4a}\)=-tan22a
Giúp mình vs! Mình đang cần gấp :((
Chứng minh:
tan3a+tan2a+tana=tan3a*tan2a*tana
Chứng minh:
tan3a-tan2a-tana=tan3a*tan2a*tana
Chứng minh rằng: cot2a + tan2a= \(\frac{2\cos4a+6}{1-\cos4a}\)
3; cho tana-cota=3 . tính giá trị các biểu thức sau :
a; A= tan2a + cot2a
Chứng minh rằng:
1 + 4cosa + 6cos2a + 4cos3a + cos4a = \(16\cos2a.\cos^4\frac{a}{2}\)
chứng minh rằng
a) \(cos^4a+sin^4a-6sin^2a.cos^2a=cos4a\)
b) \(tan\frac{3\pi}{5}-tan\frac{2\pi}{5}-tan\frac{\pi}{5}=tan\frac{\pi}{5}.tan\frac{2\pi}{5}.tan\frac{3\pi}{5}\)
\(\frac{sin2a-c\text{os}2a}{sin2a-c\text{os}2a}=tan4a-\frac{1}{c\text{os}4a}\)
Chứng minh rằng
\(\frac{1+\cos A}{2a}+\frac{1+\cos B}{2b}+\frac{1+\cos C}{2c}=\frac{27r}{8S}\)
chứng minh rằng
\(\frac{2}{sin4x}\) - tan2x = cot2x