2.5平面向量应用举例
2.5平面向量应用举例
复习 a·b=a‖b|cosO a·b=x1x2+y1y2 (1)|a=5,|b=6,θ=30°,ab=153 (2)a=(1,5),b=(3,-2),a·b=-7
复习 a b =| || | a b cos (1) | | 5, | | 6, 30 a b a b = = = = ， 15 3 a x x y 1 2 1 2 b = + y (2) (1,5), (3, 2), a b a b = = − = −7
复习 a⊥b冷a·b=0 a·b=a‖b|cosb =a‖b|cos90° =a‖b|×0
复习 a b a b ⊥ = 0 2 2 a a =| | ? a b =| || | a b cos =| || a b | cos90 =| || a b |0 = 0
复习 j→→
复习 1 1 i j x y 2 i = 2 | | i | | 1 i = | | 1 j = = 1 2 j = 2 | | j = 1 i j = 0 j i = 0
复习:坐标表示模 已知a=(x,y),求|a la=vx+y
复习：坐标表示模 已知 求 a x y a = ( , ), | | 2 2 | | a x y = +