Bài 1: Cho $\frac{sin^{4}(x)}{a}+\frac{cos^{4}(x)}{b}=\frac{1}{a+b}$.
CMR $\frac{sin^{8}(x)}{a^{3}}+\frac{cos^{8}(x)}{b^{3}}=\frac{1}{(a+b)^{3}}$
Bài 2: Tính $cos\frac{\pi}{12}\cdot cos\frac{9\pi}{12}+cos\frac{9\pi}{12}\cdot cos\frac{17\pi}{12}+cos\frac{17\pi}{12}\cdot cos\frac{\pi}{12}$
Bài 3: CMR $\frac{sin(a-b)}{sina\cdot sinb}+\frac{sin(b-c)}{sinb\cdot sinc}+\frac{sin(c-a)}{sinc\cdot sina}=0$
Bài 4: CMR $tanA+tan(A+60)+tan(a-60)=3tan(3A)$
Bài 5: $\forall \Delta ABC$.
CMR $tan\frac{A}{4}+tan\frac{B}{4}+tan\frac{C}{4}+tan\frac{A}{4}\cdot tan\frac{B}{4}+tan\frac{B}{4}\cdot tan\frac{C}{4}+tan\frac{C}{4}\cdot tan\frac{A}{4}=1+tan\frac{A}{4}\cdot tan\frac{B}{4}\cdot tan\frac{C}{4}$
Edited by DangHongPhuc, 22-11-2016 - 19:39.
