Question

( cot (A+B)=(operatorname{Cot} A C O t B-1) /(C O t A+C O t B) )
We know...... ( cot (45)=1 )
so, ( 1=(cot A cot B-1) /(cot A+cot B) )
( operatorname{Cot} A operatorname{Cot} B-1)=(operatorname{Cot} A+operatorname{Cot} B) )
( operatorname{Cot} A operatorname{Cot} B-cot A-cot B=1 )
adding 1 to both sides.....we get
( (cot A-1)(cot B-1)=2 ldots ldots ) proved

# Illustration 7. If A + B = 45°, show that (cot A - 1)(cot B - 1) = 2.

Solution