神马作文网两道三角恒等变换题目（需要解释）
来源：学生作业帮 编辑：神马作文网作业帮 分类：数学作业 时间：2024/11/10 12:41:54
两道三角恒等变换题目（需要解释）
一.（1/sin10°）-（根号3/sin80°)=
二.若tanα=1/3,则cos2α=
一.（1/sin10°）-（根号3/sin80°)=
二.若tanα=1/3,则cos2α=
1/sin10°-√3/sin80°
=1/sin10°-√3/cos10°
=(cos10°-√3sin10°)/sin10°cos10°
=2(1/2cos10°-√3/2*sin10°)/sin10°cos10°
=2cos(10°+60°)/sin10°cos10°
=4cos70°/sin20°
=4sin20° /sin20°
=4
tanα=1/3,
cos2α
=[1-(tanα)^2]/[1+(tanα)^2]
=[1-(1/3)^2]/[1+(1/3)^2]
=(8/9)/(10/9)
=8/10
=4/5
=1/sin10°-√3/cos10°
=(cos10°-√3sin10°)/sin10°cos10°
=2(1/2cos10°-√3/2*sin10°)/sin10°cos10°
=2cos(10°+60°)/sin10°cos10°
=4cos70°/sin20°
=4sin20° /sin20°
=4
tanα=1/3,
cos2α
=[1-(tanα)^2]/[1+(tanα)^2]
=[1-(1/3)^2]/[1+(1/3)^2]
=(8/9)/(10/9)
=8/10
=4/5