1) If sin(π/4 - θ) = 5/13, then cos(π/4 - θ) = 12/13.

Again sin(π/4 - θ) = sin[π/2 - (π/4 + θ)] = cos(π/4 + θ)

coa2θ= sin(π/2 - 2θ) = 2sin(π/4 - θ)cos(π/4 - θ)

Substitue hese values and find the result.

2) B = 2A

So sinB = sin2A = 2sinAcosA.

Now proceed.