Toán Chứng minh rằng $sin^{2}x$.tanx + $cos^{2}x$.cotx + sin2x = tanx + cotx 13/10/2021 By Alice Chứng minh rằng $sin^{2}x$.tanx + $cos^{2}x$.cotx + sin2x = tanx + cotx
VT=sin²x.$\frac{sinx}{cosx}$+cos²x.$\frac{cosx}{sinx}$ +2sinxcosx =$\frac{sin^4x+cos^4x}{sinxcosx}$+2sinxcosx =$\frac{(sin²x+cos²x)²-2sin²xcos²x+2sin²xcos²x}{sinxcosx}$ =$\frac{1}{sinxcosx}$ =$\frac{sin²x+cos²x}{sinxcosx}$ =tanx+cotx Trả lời
VT=sin²x.$\frac{sinx}{cosx}$+cos²x.$\frac{cosx}{sinx}$ +2sinxcosx
=$\frac{sin^4x+cos^4x}{sinxcosx}$+2sinxcosx
=$\frac{(sin²x+cos²x)²-2sin²xcos²x+2sin²xcos²x}{sinxcosx}$
=$\frac{1}{sinxcosx}$ =$\frac{sin²x+cos²x}{sinxcosx}$ =tanx+cotx