sin3x/sinx+cos3x/cosx

sin(3x)/sinx +cos(3x)/cosx
=[sin(3x)cosx+cos(3x)sinx]/(sinxcosx)
=sin(3x+x)/[(1/2)sin(2x)]
=2sin(4x)/sin(2x)
=4sin(2x)cos(2x)/sin(2x)
=4cos(2x)

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16. Given the vector α = (cosx, SiNx), B = (√ 2, √ 2), a · B = 8 / 5, then the value of Tan (x - π / 4) is
17. If x is less than or equal to 90 degrees, greater than or equal to 0 degrees, SiNx * cosx = 1 / 2, then 1 / (1 + SiNx) + 1 / (1 + cosx) =? Detailed process! I'll collect it in an hour
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