Question

Sa se determine unghiul vectorilor :
a) a = i + j
    b = i - j 
b)
a(4 , -3)
b = 3i + 4j

Answer 1

a) cos u=(1-1)/√1^2+1^2)*[√(1^2+(-1)^2]=0 => u= 90 grade

b) cos u=(4*3-3*4)/[√(16+9)^2  * √(9+16)^2]=0=> u=90 grade

Formula:
a=xi+yj
b=x`i=y`j

cos u=$\frac{xx`+yy`}{ \sqrt{x^{2}+ y^{2} } * \sqrt{x`^{2}+ y`^{2}} }$