已知X是锐角sinx=7/8sinb tanx=1/4tanb求X

sinx/cosx=sinb/(4cosb)
7sinb/8cosx=sinb/(4cosb)
7/8cosx=1/(4cosb)
8cosx/7=4cosb
8cosx=28cosb
2cosx=7cosb
cosx=7/2cosb
sinx=7/8sinb
1=49/4cos^2b+49/64sin^2b
784cos^b+49sin^2b=64
16cos^2b+sin^2b=64/49
形成方程:cos^b+sin^2b=1,16cos^2b+sin^2b=64/49
-15cos^2b=1-64/49
-15cos^2b=-15/49
cos^2b=1/49
cosb=±1/7
∵x是锐角
∴cosb>0
cosb=1/7
sinb=4√3/7
sinx=7/8sinb=√3/2
x=60度

tgx=1/4tgb
→sinx/cosx/（sinb/cosb）=1/4
→(sinx/sinb)*(cosb/cosx)=1/4
又sinx=7/8sinb→sinb=8/7sinx..1
∴cosx=7/2cosb→cosb=2/7cosx..2
对式1，2两侧平方，并相加得到
64/49sin^2x+4/49cos^2x=1
把cos...