cos A B 2 1 9, sin A 2 B 2 3, A is the second quadrant angle, B is the first quadrant angle, cos A B

I don't know specifically, but there are actually two heroes who say that they are right, and I can't refute it, so I'll talk about the basic algorithm for middle school students.

cos(a+b)=cos[2(1/2(a+b))]=cos[1/2(a+b)]^2-sin[1/2(a+b)]^2

This converts a+b to 1 2 (a+b).

And 1 2(a+b) = (a-b 2)-(a 2-b).

This connects the above formulas.

Consider using the sine and angle formulas.

sin[（a-b/2）-(a/2-b)]=sin(a/2-b)cos(a-b/2)-sin(a-b/2)cos(a/2-b)=sin[1/2(a+b)]

It should be noted that a is the second quadrant angle and b is the first quadrant angle.

cos(a-b 2)=-1 9 So a-b 2 is the second quadrant sin(a 2-b)=2 3 a 2-b is the first quadrant.

Pay attention to the plus and minus signs when calculating the corresponding sine and cosine after the sum angle.

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But the complete thing is.

cos[2 arccos[-(1/9)] 2 arcsin[2/3]]

The numerical solution is.

Hello. The answer I calculated was -239 729, which should be correct

Angle a is the second quadrant angle, and sina = 12 13

Get cosa = -5 13

sin²(πa)-cos(π+a)=sin²a+cosa=(12/13)^2-5/13=79/169

Since a is the second quadrant angle, then cos(a) <0 and sin(a) >0.

According to the periodicity of trigonometric functions, there are:

cos(3 +a) =cos( a) =cos(a) combined with cos(a) <0 to get:

cos(3 +a) = cos(a) >0 Therefore, the value of cos(3 +a) is positive, and the specific value needs to know the size of a in order to calculate.

cos(3 +a)=cos(+a)=-cosa, mainly to examine the simplification of the induction formula,

If the state selling ridge a is the second quadrant angle of the finch, then [sin(180°-a)+cos(a-360°)]2 tan(180°+a).

Induced sail infiltration formula.

sin(180°-a）=sina

cos(a-360°)=cosa

tan(180°+a)=tana

Original = (sina + cosa) 2 tana

1+2sinacosa/tana

1/tana+2(cosa)^2

sina = 15 17, so cosa = plus or minus 8 17, because a is the angle of the second quadrant, so cosa = -8 17

cos(pie 3-a)=cos60°cosa+sin60°sina=1 2*-8 17+2 roots of three times 15 17=(15 roots three-8) 34,4, known sina = 15 17, a is the angle of the second elephant to do the trillion concession, then cos(pie 3-a)=how much?

I don't know how to calculate the pure game.,I hope someone can help me write down the steps, okay?

The A angle belongs to the second quadrant, 2k + 2 4k + a < 4k + 3

2k + 2 intersects to get 4k +3 2

|cosa/2|=-cos(a 2) knows that cos(a 2) is negative, and according to the Bagua diagram, it should be in the third quadrant.