求值：1/2(csc10)-2sin70
热心网友
我试一下1/2(csc10)-2sin70=[1/(2sin10)]-2sin70=[1-4sin10*sin70]/[/(2sin10)]={1+2[cos(10+70)-cos(10-70)]}/[(2sin10)]=[1+2(cos80-cos60)]/[(2sin10)]=[1+2(cos80-0.5)]/[(2sin10)]=(1+2cos80-1)/[(2sin10)]=2cos80/[(2sin10)]=1
热心网友
1/2(csc10)-2sin70=1/(2sin10)-2sin70=(1-4sin10sin70)/(2sin10)={1+2[cos(70+10)-cos(70-10)]}/(2sin10)=(1+2cos80-2cos60)/(2sin10)=(1+2cos80-1)/(2sin10)=2cos80/(2sin10)=2sin10/(2sin10)=1