若|a|=4,|b|=5,a与b的夹角为π/3,求|a-b|及|a+b|是向量a，

Question

若|a|=4,|b|=5,a与b的夹角为π/3,求|a-b|及|a+b|
是向量a，

Answer 1

|a|=4,|b|=5,a与b的夹角为π/3,
∴a*b=4*5*1/2=10,
|a-b|^2=a^2+b^2-2a*b=16+25-20=21,
∴|a-b|=√21.
同理|a+b|^2=61,|a+b|=√61.