If α is the fourth quadrant angle and cos α = 35, then sin α equals () A. 45B. −45C. 35D. −35

If α is the fourth quadrant angle and cos α = 35, then sin α equals () A. 45B. −45C. 35D. −35

∵ α is the fourth quadrant angle, and cos α = 35, ∵ sin α = - 1 − Cos2 α = - 45

If θ is the angle of the second quadrant, then cos (sin θ) is greater than or less than 0?

If θ is the angle of the second quadrant, then 0

The number of solutions of Z ^ 2 + 5 | Z | + 6 = 0 in complex set? A; 2 B; 4C; 6D; 8

It is known that the axis of symmetry of the parabola y = ax ^ 2 + BX + C is x = 2, and the intersection points of the parabola y = ax ^ 2 + BX + C and the x-axis are located between the intervals - 1, 0, 4 and 6 respectively, and less than 0

Axis of symmetry x = - B / 2A = 2,
B = - 4A
-1, y = A-B + C = 5A + C
0 into the equation, y = C
We get C + I * a = 0 (5 > = I > = 0)
c=-ia
5b/4c=20/4i=5/i
5b>=4c

It is known that 3A = 5B + 2c, 3A / 2 + 1B / 2 = 4C and C ≠ 0
(1) Find a: B: C
(2) Find (2a + 3b-4c) of (3a-2b + 5C)

It's (3 / 2) a and (1 / 2) B.........

Given sin (a + b) sin (a-b) = - 1 / 3, find the value of COS ^ 2a-cos ^ 2B

If cos (α + β) cos (α - β) = 13, then the value of Cos2 α - sin2 β is ()
A. -23B. -13C. 13D. 23

∵ cos (α + β) cos (α - β) = 12 (Cos2 α + Cos2 β) = 13, ∵ Cos2 α + Cos2 β = 23 & nbsp; Cos2 α - sin2 β = Cos2 α + 12 − 1 − Cos2 β 2 = Cos2 α + Cos2 β 2 = 13, so C

How to do cos (a + b) cos (a-b) = cos ^ 2a-sin ^ 2B?
prove.
I teach myself at home
Oh, I don't know.
Now I only know and look up the formula
How to prove it from the right?
The most important thing is to tell me how to solve the problem.

The integration of COS (a + b) cos (a-b) and the difference expansion are carried out
cos(a+b)cos(a-b)
＝1/2（cos2a+cos2b)
=1/2(2cos^2a-1+2cos^2b-1)
=cos^2a+cos^2b-1
=cos^2a+(1-sin^2b)-1
=cos^2a-sin^2b

Given sin (a + b) sin (B-A) = m, try to find the value of COS ^ 2a-cos ^ 2B

Sin (- α) = 1 / 5, cos (π + α) is?
Please give the correct steps

sin(-α)=1/5
That is - sin α = 1 / 5
∴ sinα=-1/5
∵ cos²α=1-sin²α=1-1/25=24/25
∴ cosα=±2√6/5
∴ cos(π+α)=-cosα=±2√6/5