Let cos(a + b) = 4/5 and let sin(a - b) = 5/13 where 0 ≤ a,b ≤ π/4. Then tan 2a is

- 20/17
- 25/16
- 56/33
- 19/12

**Answer**

cos(a + b) = 4/5

tan(a + b) = 3/4

sin(a - b) = 5/13

tan(a - b) = 5/12

tan 2a = tan[(a-b) + (a+b)]

= tan(a+b) + tan(a-b)/[1 - tan(a+b)tan(a-b)]

**The correct option is C.**