1.2=5sin(a)-2sin(b-a) --- 1
-1.3=4sin(b)-2sin(a-b) --- 2

令
Sin(a) = x
Sin(b) = y
Cos(a) = [1-x^2]^(1/2)
Cos(b) = [1-y^2]^(1/2)

1:
1.2 = 5Sin(a) - 2Sin(b-a) = 5Sin(a) - 2Sin(b)Cos(a) + 2Cos(b)Sin(a)

2:
-1.3 = 4Sin(b) - 2Sin(a-b) = 4Sin(b) - 2Sin(a)Cos(b) + 2 Cos(a)Sin(b)

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