Question 392042
This trig problem involves trig identities and double angle formulas. You should start with
1. tan (4a - b) = tan4a - tanb / 1 + tan4a tanb
2. tan4a = 2tan2a / 1-2tan^2 a
3. tan2a = 2tana / 1- tan^2a
     = 2(1/5) / 1 - (1/25)
     = (2/5) / (24/25)
     = 5/12
4. tan4a = 2tan2a / 1-2tan^2 a
     = 2(5/12) / (1 - 25/144)
     = (5/6) / (119/144)
     = 120/119
5. tan (4a - b) = tan4a - tanb / 1 + tan4a tanb
     = (120/119) - (1/239) / 1 + (120/119)(1/239)
     = (28561/28441) / 1 + 120/28441
     = (28561/28441) / (28561/28441)
     = 1