设三角形ABC,直角为C,B=85°,A=5°,直角边长a和b,b=2.5m,斜边长为c,根据正弦定理有
c/sinC=b/sinB=a/sinA
则c=2.5/sin85°
a=2.5sinA/sinB=2.5sin5°/sin85°.