1)cosB= 3/5 is greater than sinA= 5/ 13, so it is an acute obtuse triangle A, sinB= 4/5, COSA =12 (SIN 2+COS 2 =1) SINC = SIN (A+)

2) SIN-α-β) COS α-COS (β-α) SIN α = 3/5β is the third quadrant angle, so cos(β)= minus 4/5 and then take the formula sin(β+ 5/4 faction) = 65438+7 and multiply it by the root number 2.

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