Question

sin15°=？

A √6+√2 / 4
B -√6+√2 / 4
C √6-√2 / 4
D -√6-√2 / 4
怎么算出来的
详细一些

Answer 1

“^2”表示平方
sin15°=cos75°
cos150°=2(cos75°)^2-1
-√3/2+1=2(cos75°)^2
(cos75°)^2=(2-√3)/4
(cos75°)^2=(4-2√3)/8
(cos75°)^2=[(√3-1)^2]/(2√2)^2
(cos75°)^2=[(√3-1)/2√2]^2
(cos75°)^2=[(√6-√2)/4]^2
cos75°>0所以cos75°=(√6-√2)/4
选C

Answer 2

1-2(sin15)^2=cos30=√3/2
(sin15)^2=(2-√3)/4
选C sin15>0

Answer 3

sin15=sin(45-30)
=sin45cos30-sin30dos45
=√2/2×√3/2-1/2×√2/2
=√6/4-√2/4
=（√6-√2）/4
应该选C吧

Answer 4

sin15°=cos75°=cos(45°+30°)
=cos45°cos30°-sin45°sin30°
=√6-√2 / 4
选C

Answer 5

选c