Question

Cos 105 how to solve
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Answer 1

Answer:

Step-by-step explanation:

y=cos(105°)

y=cos (90°+15°)

y=-sin(15°) since cos (90°+A)=-sinA

Consider sin(15°)=sin(45°-30°)

Sin(A-B)=sinAcosB-cosAsinB

Sin(45°-30°)=sin(45°)cos(30°)-cos(45°)sin(30°)

Sin(15°)=(1/√2)(√3/2)-(1/√2)(1/2)

Sin(15°)=√3/(2√2) -1/(2√2)

Sin(15°)=(√3–1)/(2√2)

Sin(15°)=(√6-√2)/4

y=-sin(15°)=cos(105°)

y=(√2-√6)/4