Question

1-tan20°×tan25°=tan20°+tan25°​

Answer 1

Bring LHS to rhs

then u will get

1=(tan20+tan25)/1-tan20×tan25

so its in tan(A+B) form which is tan(20+25)=tan45=1 hence proved

Answer 2

Solution :- As we know that ,
Tan( A + B ) = tanA + TanB / 1 - TanA*TanB
similarly,

Tan45° = Tan ( 20° + 25°) = Tan20° + tan25°/1- Tan20°Tan25°


1 = tan20° + tan25° / 1 - tan20° tan25°

1 - tan20° tan25° = tan20° tan25° Answer ✔