已知X是锐角sinx=7/8sinb tanx=1/4tanb求X

问题描述:

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=4cosb8cosx=28cosb2cosx=7cosbcosx=7/2cosbsinx=7/8sinb1=49/4cos^2b+49/64sin^2b784cos^b+49sin^2b=6416cos^2b+sin^2b=64/49形成方程:cos...