tg(A+B)=(tgA+tgB/(1-tgA.tgB))=(1/3+(1/5))/(1-(1/3)(1/5))=4/7 tg(C+D)=(tgC+tgB/(1-tgC.tgB))=(1/7+(1/8))/(1-(1/7)(1/8))=3/11logo: tg(A+B+C+D)=4/7+(3/11)/(1-(4/7)(3/11))=1,como todos os arcos estao no prim.quadrante ,tg(...)...temos: tg(A+B+C+D)=1A+B+C+D=...