= 81° + a° + a° = 180° ( angle sum property )
[tex]81° + 3a = 180° \\ 3a = 180 - 81 \\ 3a = 99 \\ a = \frac{99}{3} \\ a = 33°[/tex]
The three angles of this triangle are :
[tex] \: ∠1 \:= 81° \\ \: \: ∠2 = 2a = 2 \times 33 = 66° \\ ∠3 = a = 33 \\ \\ ∴ \: a = 33° \: [/tex]
