tan(x+π÷4）=1+tanx÷1-tanx
tanx+tanπ÷tan4=1+tanx÷1-tanx
tan（x+π÷4）=(1+tanx)÷(1-tanx)
tanx+tan1=tanx+1/1-tanx
tanx+tan1785=tan(x+1)
tan(x+1)=tan(x+1)