tan(b+45)=tan[(a+b)-(a-45)]
=[tan(a+b)-tan(a-45)]/[1+tan(a+b)tan(a-45)]
=(1/2+1/3)/(1-1/2*1/3)
=1
a+b=a-45°+b+45°
tan(a+b)=[tan(a-45°)+tan(b+45°)]/[1-tan(a-45°)tan(b+45°)]=1/2
[-1/3+tan(b+45°)]/[1+tan(b+45°)/3]=1/2
-1/3+tan(b+45°)=1/2+tan(b+45°)/6
5/6tan(b+45°)=5/6
tan(b+45°)=1
tan(b+45)=tan(( a+b)-(a-45))=(tam(a+b)-tan(a-45))/(1-tan(a+b)*tan(a-45))
=(1/2+1/3)/(1+5/6)=5/11
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