已知cosX=-3/5 且 π小于X小于3π/2 则tan(X-π/4)
问题描述：
已知cosX=-3/5 且 π小于X小于3π/2 则tan(X-π/4)
答
sinx= - 4/5
tanx=4/3
tan(x-π/4)
=(tanx - tanπ/4)/(1 + tanx tanπ/4)
=1/7
答
因为cosx=-3/5,π＜x＜3π/2
所以sinx=-√[1-(cosx)^2]=-√[1-(-3/5)^2]=-4/5
所以tanx=sinx/cosx=4/3
所以tan(x-π/4)
=[tanx-tan(π/4)]/[1+tanx*tan(π/4)]
=(4/3-1)/(1+4/3)
=1/7