One high school trigonometric question, one high school trigonometric question

Landlord.,It's very troublesome to write this on this.。。 It's not good for you to leave a QQ?。。 The probability of this kind of question in the college entrance examination is not very large.

There are a lot of them in the workbook. I'm a student of this year's college entrance examination. It is recommended that you get the foundation firm, so that there is no problem at all

The vector m is stupid and stupid and is stupid and stupid is straighter than the vector n, so m·n=0, i.e., x1x2+y1y2=0.

(sinb+sinc)(sinb-sinc)+(sina-sinb)[sin(b+c)]=0

(sinb+sinc) (sinb-sinc) and (sina-sinb)[sin(b+c)] need to be equal to 0 at the same time

Because in the triangle, the sins of the angles a, b, and c are all greater than zero, so sinb+sinc is greater than 0

sin(b+c) is also greater than zero.

This requires: sinb-sinc=0

sina-sinb=0

You can get sina=sinb=sinc

If all three angles are acute, you can get a=b=c, so the angle c=60 degrees.

If one of them is an obtuse angle, let a be an obtuse angle, then b=c is an acute angle.

Since sina = sin( -a), then -a=b=c, so that the sum of the three angles =a+b+c=a+ -a+ -a=2 -a=180 degrees.

The solution is a = 180 degrees, which does not meet the requirements of the triangle, so this triangle can only be a triangle with sharp corners.

So the angle c = 60 degrees.

(2sin80-cos70)/cos20

2sin(60+20)-sin20]/cos20=[2(sin60cos20+cos60sin20)-sin20]/cos20

2sin60cos20+2cos60sin20-sin20)/cos20

Because cos60 = 1 2

So, the original formula = (2sin60cos20 + 2 1 2sin20-sin20) cos20

2sin60cos20+sin20-sin20)/cos20=(2sin60cos20)/cos20

2sin60

3. Happy studying.

1) f(x)=sinwxcoswx+1 2cos2wx+1 21 2sin2wx+1 2cos2wx+1 sloac2 2 2( 2 2sin2wx+ 2 2cos2wx)+1 蚂wuyou2 2 2sin(2wx+ 4)+1 2

2w=2∏/t=2 ∴w=1

2) The function image of g(x) = 2 2sin(4x+ 4)+1 2g(x) increases monotonically in the interval [0, 16], and the orange is high, so g(x) obtains the minimum value at x=0 g(x)min= 2 2sin(0+ 4)+1 2=1 2+1 2=1

f(x)=sin2 x+cos2 x= 2sin(2 x+ 4) period t=2 2 = so =1

f(x) = 2sin (2x + 4).

g(x) = 2sin(4x+ ascending mega handicap 4)g(x)min=g(0)=1

You don't have to read anymore. Brain-dead.