a) Ta có: sin 105⁰ = sin(180⁰-105⁰) => sin 105⁰= sin 75⁰

b) cos170⁰= -cos(180⁰-170⁰) => cos170⁰ = -cos10⁰

c) cos122⁰ = -cos(180⁰-122⁰) => cos122⁰ = -cos58⁰

a) Ta có: sin 105⁰ = sin(180⁰-105⁰)                 =>   sin 105⁰= sin 75⁰

b)          cos170⁰= -cos(180⁰-170⁰)                 =>   cos170⁰ = -cos10⁰

c)          cos122⁰ = -cos(180⁰-122⁰)                =>    cos122⁰  = -cos58⁰

\(\sin75\)

\(sin75=\frac{\sqrt{6}+\sqrt{2}}{4}\)

nhớ k đấy

\(\sin75=\frac{\sqrt{6}+\sqrt{2}}{9}\)

Lấy mấy tính mà tính chứ ko biết cách làm

Chọn A.

Ta có:

\(sin15^o+sin75^o-cos15^o-cos75^o+sin30^o\)

\(=\left(sin15+sin75^o\right)-\left(cos15^o+cos75^o\right)+sin30^o\)

\(=\dfrac{\sqrt{6}}{2}-\dfrac{\sqrt{6}}{2}+\dfrac{1}{2}\)

\(=0+\dfrac{1}{2}\)

\(=\dfrac{1}{2}\)

\(sin15^o+sin75^o-cos15^0-cos75^o+sin30^o\)

\(=cos75^o+cos15^0-cos15^0-cos75^o+sin30^o\)

\(=sin30^o=\dfrac{1}{2}\)

A=sin 15⁰+sin 75⁰-sin 75⁰-sin 15⁰+sin 30⁰

A=sin 30⁰=\(\dfrac{1}{2}\)=0,5

vì cos 15⁰=sin (90⁰-15⁰)=sin 75⁰

cos 75⁰=sin (90⁰-75⁰)=sin 15⁰