1. ( sinA )2 + (cosA)2 = 1
2. (tanA)2 + (cotA)2 = 1
3. SinA = 1 /cosecA
4. CosA = 1 /secA
5. TanA = 1/cotA (also inverse as secA= 1/ CosA)
6. sin2a = 2 sinA CosA
7. cos2a = (cosa)2 - (sina)2
= 2(cosa)2 - 1
= 1 - 2 (sina)2
8. tan2a = 2tana / 1- (Tana)2.