ANSWER QUICK PLEASE

sqrt(2)/2  which is choice D

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Explanation

(3pi/4) radians converts to 135 degrees after multiplying by the conversion factor (180/pi).

The angle 135 degrees is in quadrant 2. We subtract the angle 135 from 180 to find the reference angle

180-135 = 45

Then you can use a 45-45-90 triangle to determine that the ratio of opposite over hypotenuse is sqrt(2)/2

sine is positive in quadrant 2

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Alternatively, you can use a unit circle. Refer to the diagram below. In red, I've circled the angle 3pi/4 radians. The terminal point for this angle has a y coordinate of sqrt(2)/2

Recall that y = sin(theta).