Calculation: cos 275 ° + cos 215 ° + cos 75 ° cos 15 °

Calculation: cos 275 ° + cos 215 ° + cos 75 ° cos 15 °

cos75°=cos（45°+30°）=cos45°cos30°-sin45°sin30°=6-24．cos15°=cos（45°-30°）=cos45°cos30°+sin45°sin30°=6+24． cos275°+cos215°+cos75°cos15°=cos275°+sin275°+6-24•6+24=1+14=54．...

Calculation: cos 275 ° + cos 215 ° + cos 75 ° cos 15 °

cos75°=cos（45°+30°）=cos45°cos30°-sin45°sin30°=
6-
Two
4．
cos15°=cos（45°-30°）=cos45°cos30°+sin45°sin30°=
6+
Two
4．
cos275°+cos215°+cos75°cos15°=cos275°+sin275°+
6-
Two
4•
6+
Two
4=1+1
4=5
4．

COS75^2+cos15^2+COS75COS15=? To process

cos75^2+cos15^2+cos75cos15
=sin15^2+cos15^2+sin15cos15
=1+1/2*sin30
=1+1/2*1/2
=5/4

Known vector a=（3，4）， B = (sin α, cos α), and a⊥ b. Then Tan α is () A. 3 Four B. 4 Three C. -3 Four D. -4 Three

∵ vector
a=（3，4），
B = (sin α, cos α), and
a⊥
b，
ν 3sin α + 4cos α = 0, i.e. sin α
cosα=-4
3，
Then Tan α = - 4
3．
Therefore, D is selected

Known vector a=（4，3）， B = (sin α, cos α), and a∥ b. So tan2 α=______ .

∵ vector
a=（4，3），
B = (sin α, cos α), and
a∥
b，
ν 4 × cos α - 3 × sin α = 0, sin α = 4
3cosα，
That is, Tan α = sin α
cosα=4
3．
∴tan2α=2tanα
1−tan2α=2×4
Three
1−(4
3)2=-24
7．
So the answer is: - 24
7．

Given a vector a = (COS α, - 2), B = (sin α, 1), and a / / B, then Tan (α - π / 4) =? A.3 B.-3 C.1/3 D.-1/3

cosa/-2=sina/1
-0.5=sina/cosa
tana=-0.5
tan(a-π/4)=(tana-tanπ/4)/(1-tana*tanπ/4)=(tana-1)/(1-tana)=-2.25

The square of sin + the square of COS =?

The square of sin + the square of COS = 1. This is obtained from the Pythagorean theorem. If you draw a right triangle, the two right sides are represented by the hypotenuse. The result is: hypotenuse × Sina square + oblique edge × cosa square = hypotenuse square

It is known that sin (a + π / 4) = 1 / 3 and π / 2 Math homework help users 2017-11-02 report Use this app to check the operation efficiently and accurately!

cos(3π/4-a)
=cos(a-3π/4)
sin(a+π/4)
=sin(a+π-3π/4)
=-Sin (A-3 π / 4). Induction formula
=1/3
∵π/2

If sin (π + a) = 1 / 2, then the value of COS (3 / 2 π - a) is?

sin(π+A)=-sinA=-1/2
So Sina = 1 / 2
So cos (3 / 2 π - a) = cos (π + π / 2-A) = - cos (π / 2-A) = - Sina = - 1 / 2

If cos (π + a) = - 1 / 2,3 / 2 π Homework help users 2016-12-08 report Use this app to check the operation efficiently and accurately!

If cos (π + a) = - 1 / 2,3 / 2 π cosa = 1 / 2
Then sin (2 π + a)
=sina
=-√ (1-cos square a)
=-√(1-1/4)
=-√3/2