Two vectors have magnitudes 3 unit and 4 unit respectively. What should be the angel between them if the magnitude of the resultant ils a. 1 unit, b. 5 unit and c. 7 unit.

Answer

A, B, C

Explanation

`vec|a|=3`
& `|vecb|=4`
(a). If R= 1 unit
then `sqrt(3^2+4^2+2.3.4 cos (theta))=1`
`rarr 25+24 cos (theta) =1`
`rarr 24 cos theta = -24`
`rarr cos theta= -1`
`rarr theta = 180^0`
(b).`sqrt(3^2+4^2+2.3.4 cos theta)=7`
`rarr 25+24 cos theta=49`
`rarr 24 cos theta=24`
`rarr cos theta =1`
`rarr theta =cos^-1(1)=0^@`
Hence angle between them is `0^@`.