=√(a^2+b^2+2ab)=√(9+ 16+2*3*4* 1/2)=√37.
The modulus of vector a-b = √ (a-b) 2 = √ (a-b) 2.
=√(a^2+b^2-2ab)=√(9+ 16-2*3*4* 1/2)=√ 13.
(2) Cosine of the included angle @ between vector a+b and vector a-b = (A-B) * (A+B)/(| A-B || | A+B |)
=(a^2-b^2)/(|a-b||a+b|)=-7/√(37* 13).