On the scalar product of several vectors (1) |a | = 2, B = (- 2,4), and a ⊥ B, then a coordinate of a is_______ (2) Given a = (5,8), B = (2,3), C = (1, - 2), then (a * b) * C=___________ (3) Given that | a | = 8, a * b = - 12, then the number of projections of B in a direction is_____________

On the scalar product of several vectors (1) |a | = 2, B = (- 2,4), and a ⊥ B, then a coordinate of a is_______ (2) Given a = (5,8), B = (2,3), C = (1, - 2), then (a * b) * C=___________ (3) Given that | a | = 8, a * b = - 12, then the number of projections of B in a direction is_____________

1) . a = (x, y), X ` 2 + y ` 2 = 2, - 2x + 4Y = 0, the solution is x = 2 * radical 0.4, y = radical 0.4. So a = (2 * radical 0.4, radical 0.4)
2).a*b=5*2+8*3=34,(a*b)*c=34*c=(34,-68)
3) According to the definition of vector product, we can know that a * b = cos @ | a | * | B | = 8cos @ * | = - 12
|8cos @ * | B | = | - 12 / 8 | = 1.5