Answer:
Formula:(from trigonometry)
Tan(A+B)=(tanA+tanB)/(1-tanA*tanB)
Let A=22 degrees,B=23 degrees
Tan(22+23)=(tan22+tan23)/(1-tan22*tan23)
From trigonometry we know tan45=1
Therefore tan(45)=1=(tan22+tan23)/(1-tan22tan23)
=> 1-tan22tan23=tan22+tan23
=> tan22+tan23+tan23tan22 =1
Hence proved
