How do I find the value of tan (3Pi/4)?

##-1##

Basically when they say ##pi##, they mean ##pi## radians. ##pi ## radians = ##180^@## So, ##tan((3pi)/4)## = ##tan((3xx180^@)/4)## = ##tan((3xx45cancel(180)^@)/cancel(4))## = ##tan(3xx45^@)## = ##tan(135^@)## = ##-1##

Note: The CAST rule says that tan should be negative in the second quadrant ##(90^@ - 180^@)## Basic values of tan are tan0 = 0 tan 30 = ##1/sqrt(3)## tan45 = 1 tan60 = ##sqrt(3)## tan90 = undefined (or ##oo##)

You can add and subtract angles to and from 180 and 360 to get the same angle provided you follow the cast rule for the sign. So, ##tan(180-x) = - tanx## likewise, ##tan135=tan(180-45)=-tan45=-1##