Question

if `|vecaxxvecb|^2+|veca.vecb|^2=400 ` and `|vec a| = 5` , then write the value of `|vecb|`

Answer 1

`|vecaxxvecb|^2+|veca.vecb|^2=400 `

 `=>{|veca||vecb|sintheta}^2+{|veca||vecb|costheta}^2=400`

 `=>|veca|^2|vecb|^2sin^2theta+|veca|^2|vecb|^2cos^2theta=400`

`=>|veca|^2|vecb|^2=400`

 `=>25xx|vecb|^2=400`

`=>|vecb|^2=16`

`=>|vecb|=4`