Sin 3pi divided by 4

Sin 3pi/4 is angle 135 degrees or 45 degrees below 180 degrees. Hence it's opposite side is 1 and adjacent is 1, implying the hypothenus is sqrt (2). Hence

Sin 3pi/4 = 1/sqrt (2). Now multiply by sqrt (2) / sqrt (2) to get:

[1/sqrt (2).] * [sqrt (2) / sqrt (2) ] = sqrt2) / 2