To find the value of cos150 and tg120, we will need to use trigonometric identities and formulas:

cos150 = cos(180 - 30)
Using the cosine subtraction formula, we have:
cos(180 - θ) = -cos(θ), where θ = 30
cos150 = cos(180 - 30) = -cos30
Since cos30 = √3/2, we have:
cos150 = -√3/2

tg120 = tan120
We can find the tangent value using the tangent addition formula:
tan(90 + θ) = -cot(θ), where θ = 30
tan120 = tan(90 + 30) = -cot30
Since cot30 = √3, we have:
tg120 = -√3

Therefore, cos150 = -√3/2 and tg120 = -√3.