Question

Cos2b=-1/3 найдите cosb

Answer 1

Cos2b без 2
и всё
правильно?

Answer 2

$2 \cos ^{2} (b) - 1 = - \frac{1}{3} \\ \cos(b) = \frac{ \sqrt{3} }{3}$
По всем вопросам пишите в лс

Answer 3

To solve for cos(b) given the equation cos(2b) = -1/3, we can use a trigonometric identity. The double-angle identity for cosine states that cos(2θ) = 2cos²(θ) - 1. By comparing this identity to the given equation, we can equate the two expressions:

2cos²(b) - 1 = -1/3

Now, let's solve for cos(b):

2cos²(b) = -1/3 + 1

2cos²(b) = 2/3

cos²(b) = 2/3 * 1/2

cos²(b) = 1/3

Taking the square root of both sides:

cos(b) = ±√(1/3)

So, cos(b) can be either positive or negative square root of 1/3. Therefore, cos(b) is equal to ±√(1/3).