Given that a = (1,2) B = (- 2, n) the angle between a and B is 45 °, find B if the vector C and B are in the same direction and C-A is perpendicular to A. find C Find C If the vector C and B are in the same direction, and C-A is perpendicular to a, find C The answer is b = (- 2,6) C = (- 1,

Given that a = (1,2) B = (- 2, n) the angle between a and B is 45 °, find B if the vector C and B are in the same direction and C-A is perpendicular to A. find C Find C If the vector C and B are in the same direction, and C-A is perpendicular to a, find C The answer is b = (- 2,6) C = (- 1,

1, cos45 = (a * b) / (a module * B module)
2,b=kc （k》0）
3,（c-a）*a =0
Two unknowns and three equations

(sin10 degrees) square + (sin20 degrees) square +. + (sin80 degrees) square=

4
shiA=cos(90-A)
Sina square + cosa square = 1

1. [radical 3 (tan12 ° - radical 3)] / [2sin12 ° (2cos square 12 ° - 1)]
2. [root sign (sin2x + cos 2x)] + sin2x + (root sign 3) * cos2x

1.
[radical 3 (tan12 ° - radical 3)] / [2sin12 ° (2cos square 12 ° - 1)]
=(root 3tan12-3) / [2sin12cos24]
=[cos12 (root 3tan12-3)] / [2sin12cos24]
=(root 3sin12-3cos12) / [sin24cos24]
=(radical 3sin12-3cos12) / [1 / 2sin48]
=(radical 3sin12-3cos12) / [1 / 2Sin (60-12)]
=(radical 3sin12-3cos12) / [radical 3 / 4cos12-1 / 4sin12]
=-(radical 3) / 4
two
[radical (sin2x + cos 2x)] + sin2x + (radical 3) * cos2x
=Root [(sin2x) ^ 2 + cos ^ 2 (x)] + sin2x + root 3cos2x
=Root sign [4sin ^ 2 (x) cos ^ 2 (x) + cos ^ 2 (x)] + (sin2x + root sign 3cos2x)
=Root {cos ^ 2 (x) [4sin ^ 2 (x) + 1]} + 2Sin (2x + pi / 3)
=|Cosx | radical [4sin ^ 2 (x) + 1] + 2Sin (2x + pi / 3)