Question

chứng minh theo kiểu vt=... = vp(dpcm) giúp mình với

Answer 1

\(a,VT=\dfrac{1+cos\alpha}{1-cos\alpha}-\dfrac{1-cos\alpha}{1+cos\alpha}=\dfrac{\left(1+cos\alpha\right)^2-\left(1-cos\alpha\right)^2}{1^2-cos\alpha^2}\\ =\dfrac{1+2cos\alpha+cos^2\alpha-1+2cos\alpha-cos^2\alpha}{sin^2\alpha}\\ =\dfrac{4cos\alpha}{sin^2\alpha}\\ =4\left(\dfrac{cos\alpha}{sin\alpha}:\dfrac{sin^2\alpha}{sin\alpha}\right)\\ =\dfrac{4cot\alpha}{sin\alpha}=VP\left(dpcm\right)\)