Question

in reperul cartezian XOy se consideră punctele A (2-1) B (-1, 2)

Answer 1

OA = ($x_{O}$ - $x_{A}$)i +$( y_{0} - y_{A})$j
= -2i + j =>3*OA = 3(-2i + j) = -6i + 3j
OB = $( x_{O} - x_{B})i + ( y_{O} - y_{B})$j 
= i -2j => 2*OB = 2(i - 2j) = 2i - 4j
3*OA + 2*OB = -6i + 3j +2i - 4j = -4i -j = -1(4i + j)