Question

两个单位向量a,b的夹角为π/3,则|a+b|=?

Answer 1

|a|=1,|b|=1

|a+b|^2

=a^2+2ab+b^2

=1+2|a||b|cosπ/3+1

=1+2X1/2+1

=3

所以：|a+b|=√3