#A+B=315^@=360^@-45^@#.
#:. tan(A+B)=tan(360^@-45^@)#.
#:. (tanA+tanB)/(1-tanAtanB)=-tan45^@=-1#.
#:. tanA+tanB=-1+tanAtanB, or, #
#tanA+tanB-tanAtanB=-1..................(ast)#.
Now, #"the reqd. value="(1-tanA)(1-tanB),#
#=1-tanA-tanB+tanAtanB#,
#=1-(tanA+tanB-tanAtanB)#,
#=1-(-1).................................................[because, (ast)]#,
#rArr" The Reqd. Value"=2#.