If sin θ × cos θ < 0, the quadrant where the final edge of angle θ is located is

If sin θ × cos θ < 0, the quadrant where the final edge of angle θ is located is

Sin and COS must be different signs, sin is positive, in one, two, at this time cos should be negative, should be in two or three, there is a second quadrant for intersection, the same reason, the third quadrant also meets the conditions, to sum up, the final quadrant is in the second or third!

Given that the final edge of the angle α crosses the point (a, 2a) (a ≠ 0), find sin α, cos α

It can be compared to a right triangle
Two right angles are a, 2A,
The hypotenuse is root 5A
Sin = 2 / radical 5
Cos α = 1 / root 5
(you can resolve it by yourself)

If the point P (- sin α, cos α) is on the final edge of angle β=

Solution - Sina = sin (- a) = cos (π / 2 - (- a)) = cos (π / 2 + a) = cos (2k π + π / 2 + a)
cosα=sin（π/2+a）
So the point P (- sin α, cos α) is the point P (COS (π / 2 + a), sin (2k π + π / 2 + a))
From the point P (- sin α, cos α) on the final edge of angle β
Then β = 2K π + π / 2 + A, K belongs to Z

If the final edge of the angle passes through the point P (- 3, b) and cos α = - 3 / 5, then B =? Sin α =?

The final edge of the angle α passes through the point P (- 3, b),
If cos α = - 3 / √ [(- 3) ^ 2 + B ^ 2] = - 3 / 5, then
ν 9 + B ^ 2 = 25, B ^ 2 = 16, B = T4,
/ / sin α = soil 4 / 5

Let P (x, y) be any point on the final edge of angle A. X in brackets,

X and Y in brackets are abscissa and ordinate of point P respectively

Irregular triangle, known one angle, one side, how to use trigonometric function to find the other two sides, two angles?

Given one angle, one side can not find the other two sides, two angles
You can draw a picture for yourself

The method of finding angle by known three sides in trigonometric function

cosA=(b^2+c^2-a^2)/2bc
cosB=(a^2+c^2-b^2)/2ac
cosC=(b^2+a^2-c^2)/2ab
Cosine theorem for angles of known three sides

Given Tana = - 2 and angle a is the angle of the second quadrant, find the other five trigonometric functions of angle A

cota=-1/2
Tana = Sina / cosa Tan ^ 2A = sin ^ 2A / cos ^ 2A (simultaneous Square) Tan ^ 2A = sin ^ 2A / 1-sin ^ 2A sin ^ 2A = 4 / 5 is positive cos ^ 2A = 1 / 5 and negative

Symmetry center of trigonometric function What is the symmetry center of y = 0.5sin (2x - π / 6)

(π/12+nπ/2,0)

It is known that sin (π - α) cos (- α + 3 π / 2) / cos (- π - α), and α is the third quadrant angle. 1. Simplify f (α) 2. If cos (α + π / 2) = 1 / 5, find the value of f (α)

F (α) = sin (π - α) cos (- α + 3 π / 2) / cos (- π - α) = sin α cos (- α + 2 π - π / 2) / cos (π + α) = sin α cos (α + π / 2) / (- cos α) = sin α (- sin α) / (- cos α) = sin ^ 2 α / cos α is the third quadrant angle cos (α + π / 2) = 1 / 5-sin α = 1 / 5sin α =