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If a=hati+2hatk+3hatk, b=-hati+2hatj = hatk and c=3hati+hatj, then p such that a+pb is at right angle to c will be

Answer»

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5

Solution :Given,`a+p b ` is at right ANGLE to c.
`therefore (a+pb)*c=0 RARR a*c+p(b*c)=0`
`rArr 5-p=0 `
`[ because a*c = 3+2 = 5 and b*c=-3+2 = -1] `
`therefore p = 5`


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