Answer: c=a+b c*a=0, so c*a=(a+b)a=0 gives a 2+a * b = 0.
A 2 = 1, so A * B = | A | | B | * Cos angle = 1*2*cos angle =- 1.
The included angle of cos =- 1/2 is 120.
2. Thinking: There are two solutions to this module length problem. 1 is the coordinate, and 2 is the expansion. There are no coordinates here. We choose to expand, and expansion must be squared first.
Answer: | 3a-b | 2 = 9a2+b2-6a * b = 9 * 42+52-6a * b =144+25-6 * | a ||||| b | * cos60 =160.
Finally, don't forget the recipe: Root Sign 109.
Don't ask me anything
Willing to adopt.