三角计算1.sec50+tan10=?2.解方程cos3xtan5x=sin7x需要主要步骤,

Question

三角计算 1.sec50+tan10=?2.解方程 cos3x tan5x=sin7x 需要主要步骤,

Answer 1

1、
sec50+tan10
=csc40+cot80
=1/sin40+cos80/sin80
=(2cos40+cos80)/sin80
=[cos40+(cos40+cos80) ]/sin80
=[cos40+2cos60cos20 ]/sin80
=(cos40+cos20 )/sin80
=2cos30cos10/sin80
=2cos30
OK
2、
cos3x * sin5x= sin7x *cos5x
=>
sin 8x+ sin2x = sin12x+sin2x
=>
sin8x = sin12x
=>
8x=12x+2k*pi
or
2*pi-8x=12x+2k*pi
OK