Cgsbily
幼苗
共回答了21个问题采纳率:85.7% 举报
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
1年前
10