Question

向量m=[cosa-(√2/3),-1] n=(sina,1) m‖n且a∈(-π/2,0)

1.求sina-cosa的值
2.求(1+sin2a=cos2a)/(1+tana)的值
m‖n 平行啊

Answer 1

(1)cosa-(√2/3)=-sina
sina+cosa=√2/3
(sina+cosa)^2=2/9=1+2sinacosa,sinacosa=-7/18
(sina-cosa)^2=(sina+cosa)^2-4sinacosa=16/9
a∈(-π/2,0)
sina<0,cosa>0
sina-cosa<0
sina-cosa=-4/3

(2)1+sin2a-cos2a=2sinacosa+2sina^2=2sina(cosa+sina)
1+tana=(sina+cosa)/cosa
(1+sin2a-cos2a)/(1+tana)=2sinacosa=-7/9

Answer 2

题目写清楚点啊

Answer 3

m‖n是什么?

Answer 4

1. -4/3