What is the value of sin(−θ)sin(−θ) ?

cos ( - θ)  = cos ( θ )  = 4/5

Since  tan θ  and cos θ   >  0 , θ must be a first quadrant angle

So....sin θ  =  3/5

So.....sin (- θ)  = -sin (θ)  =  -3/5