1.

यदि ` veca = hati + 4 hatj + 2hatk , vecb = 3hati - 2hatj + 7hatk ` तथा ` vec c = 2hati - hatj + 4hatk ` , तब उस सदिश `vecp` को ज्ञात कीजिए जो दोनों ` veca " व् " becb` से लम्बवत हो तथा ` vecp . vecc = 18 `.

Answer» माना `vecp = (xhati + yhatj + zhatk) ` तथा दिया है, ` vecp bot veca , vecp bot vecb` तथा ` vecp . Vecc = 18`
`rArr vecp . veca = 0 , vecp . vecb= 0 " तथा" vecp . Vecc = 18`
अब , `(xhati + yhatj + zhatk).(hati + 4 hatj + 2hatk) = 0 `
`rArr x + 4y + 2z = 0 ` ...(1)
`(xhati + yhatj + zhatk).(3 hati - 2 hatj + 7hatk) = 0 `
`rArr 3x + 2y + 7z = 0 ` ...(2)
`(xhati + yhatj + zhatk).(2 hati - hatj + 4hatk) = 18 `
`rArr 2x - y + 4z = 18` ...(3)
समी (1) व् (2) से
`(x)/(28 +4) = (y)/(6-7) = (z)/(-2 -12) = lambda`
` rArr x =32lambda , y= - lambda " तथा" z = - 14lambda `
यह मान समी में रखने पर ` 64 + lambda - 56 lambda = 18`
` rArr 9lambda = 18 rArr lambda = 2`
` x = 64 , y= -2, z =- 28`
अतः अभीष्ट सदिश ` = 64 hati - 2hatj - 28hatk` .


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