Given the angle α = Cos2, then the quadrant of α is The focus is on the process

Given the angle α = Cos2, then the quadrant of α is The focus is on the process

The fourth quadrant
cos2 = -0.4161
So,
Angle α = -0.4161,
But notice, it's still in radians!
In order to judge the quadrant easily, convert = - 0.4161 into angle value,
-4161 (radian) = - 0.4161 * 180 / PI (angle) = - 23.8 (angle)
-23.8 (angle) this angle, of course, is in the fourth quadrant~

It is known that [x] is the largest integer not exceeding x, [sin1] + [Cos2] + [tan3] + [SiN4] + [cos5] + [tan6]=

0+(-1)+(-1)+(-1)+0+(-1)=-4

Cos2 (π / 4 + α) + Cos2 (π / 4 - α) = (2 is the square)

[cos(π/4+α)]^2+[cos(π/2-(π/4+α))]^2
=[cos(π/4+α)]^2+[sin(π/4+α)]^2
=1

Simplification of a? Cos2 π - B? Sin 3 π / 2 + abcos π - absin π / 2

=a²+b²-ab-ab
=a²+b²-2ab
=（a-b）²

Simplify (1) a square Cos2 Wu - b square sin 2 / 3 + abcos Wu - absin 2 parts (2) mtano + NCOs 2 / 1 Wu - PSIN Wu - QCOS Simplify (1) a square Cos2 Wu - b square sin 2 / 3 + abcos Wu - absin 2 parts (2) mtano + NCOs 2 parts 1 Wu - PSIN Wu - QCOS 2 parts 3 - rsin2

(1) Answer: (a-b) 2

Evaluate cos π 7cos2π 7cos4π 7= ___ .

Original formula = 2Sin π
7cosπ
7cos2π
7cos4π
Seven
2sinπ
7=1
2×2sin2π
7cos2π
7cos4π
Seven
2sinπ
7=2sin4π
7cos4π
Seven
8sinπ
7=sin8π
Seven
8sinπ
7=-sinπ
Seven
8sinπ
7=-1
8．
So the answer is: - 1
8．

Evaluation: Cos2 π 7+cos4π 7+cos6π 7．

Original formula = sin π
7(cos2π
7+cos4π
7+cos6π
7)
sinπ
Seven
=sinπ
7cos2π
7+sinπ
7cos4π
7+sinπ
7cos6π
Seven
sinπ
Seven
=1
2(sin3π
7−sinπ
7)+1
2(sin5π
7−sin3π
7)+1
2(sin7π
7−sin5π
7)
sinπ
Seven
=-1
2．

Evaluation: Cos2 Π / 7 * Cos4 Π / 7 * cos8 Π / 7 Please answer as soon as possible,

cos2∏/7*cos4∏/7*cos8∏/7
=sin2∏/7*cos2∏/7*cos4∏/7*cos8∏/7÷sin2∏/7
=1/2*sin4∏/7*cos4∏/7*cos8∏/7÷sin2∏/7
=1/4*sin8∏/7*cos8∏/7÷sin2∏/7
=1/8*sin16∏/7÷sin2∏/7
16 Π / 7 - 2 Π / 7 = 2 Π complement each other, so sin16 Π / 7 = sin2 Π / 7
So the original formula = 1 / 8

In △ ABC, if sinasinb = Cos2 (C / 2), then the following equation must be true A.A=B B.A=C C.B=C D.C=90° The answer is to choose a and find out the detailed steps to solve the problem^

According to COSC = 2cos ^ 2 (C / 2) - 1sinasinb = 0.5 * (COSC + 1) sinasinb = 0.5cos (pi-a-b) + 0.5sinasinb = - 0.5cos (a + b) + 0.5sinasinb = - 0.5cosacosb + 0.5sinasinb + 0.5sinasinb + 0.5sinasinb = 1cos (a-b) = 1A = B

Cos (α + β) = 4 / 5, cos (α - β) = - 4 / 5, α + β is in the fourth interval, α - β is in the second interval

It's a quadrant, not an interval
Analysis: ∵ cos (α + β) = 4 / 5, cos (α - β) = - 4 / 5, α + β in the fourth quadrant, α - β in the second quadrant, we may as well set a period [0,2 π],
That is, 3 π / 2 ＜ α + β ＜ 2 π, π / 2 ＜ α - β ＜ π,
∴2π＜2α＜3π,π/2＜2β＜3/2π,
/ / 2a is in the first and second quadrants; 2 β is in the second and third quadrants,
Then sin (α + β) = - 3 / 5, sin (α - β) = 3 / 5,
cos(2α)=cos[((α+β)+(α-β)]
=cos(α+β)cos(α-β)-sin(α+β)sin(α-β)
=4/5*(-4/5)-(-3/5)*3/5
=-7/25
cos(2β)=cos[((α+β)-(α-β)]
=cos(α+β)cos(α-β)+sin(α+β)sin(α-β)
=4/5*(-4/5)+(-3/5)*3/5
=-1
Because there is no analysis angle upstairs, so I did it again to help you fully understand the topic