1.

`veca,vecb` and `vecc` are three non-zero vectors, no two of which are collinear and the vectors `veca+vecb` is collinear with `vecb`, `vecb+vecc` is collinear with `veca`, then `veca+vecb+vecc=`A. `vec a`B. `vec b`C. `vec c`D. none of these

Answer» Correct Answer - D
It is given that
`vec a + vec b ` is collinear with `vec c and vec b + vec c ` is collinear with `vec a.`
`therefore vec a + vec b = lambda vec c and vec b + vec c = mu vec a `
`rArr vec a + vec b = lambda (mu vec a - vec b) " " [" On eliminating " vec c ]`
`rArr (lambda mu -1) vec a - (lambda +1) vec b = vec 0`
`rArr lambda mu -1=0 and lambda +1=0 " " [ vec a , vec b " are non- collinear "] `
` rArr lambda = -1 and mu = -1`
Substituting `lambda = -1 " in " vec a + vec b = lambda vec c , " we get " vec a + vec b + vec c = vec 0 `


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