Question

What is the value of cos(150°)?

Answer 1

Given that cos(150°).

`\cos (150^o)=\cos (180^o-30^o)`
`\text{Use }\cos (180^o-30^o)=-\cos 30^o`

`\cos (150^o)=-\cos (30^o)`
`\text{Use }\cos (30^o)=\frac{\sqrt[]{3}}{2}\text{.}`

`\cos (150^o)=-\frac{\sqrt[]{3}}{2}`

Hence the required value is

`\cos (150^o)=-\frac{\sqrt[]{3}}{2}`