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Question

Find the vector equations of the following planes in scalar product form r·n=d:
(i) r=2i^-k^+λi^+μi^-2j^-k^

(ii) r=1+s-t t^+2-s j^+3-2s+2t k^

(iii) r=i^+j^+λi^+2j^-k^+μ-i^+j^-2k^

(iv) r=i^-j^+λi^+j^+k^+μ4i^-2j^+3k^

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Solution

i We know that the equation r=a+λb+μc represents a plane passing through a point whose position vector is a and parallel to the vectors b and c.Here, a=2 i^+0 j^-k^; b=i^; c=i^-2 j^-k^Normal vector, n=b×c=i^j^k^1001-2-1=0 i^+j^-2 k^=j^-2 k^The vector equation of the plane in scalar product form isr. n=a. nr. j^-2 k^=2 i^+0 j^-k^. j^-2 k^r. j^-2 k^=2

ii The given equation of the plane isr=1+s-t i^+2-s j^+3-2s+2t k^r=i^+2 j^+3 k^+s i^-j-2 k^+t - i^+0 j^+2 k^ We know that the equation r=a+sb+t c represents a plane passing through a point whose position vector is a and parallel to the vectors b and c.Here, a=i^+2 j^+3 k^; b=i^-j-2 k^; c=- i^+0 j^+2 k^Normal vector, n=b×c=i^j^k^1-1-2-102=-2 i^+0 j^-k^=-2 i^- k^The vector equation of the plane in scalar product form isr. n=a. nr. -2 i^- k^=i^+2 j^+3 k^. -2 i^- k^r. -1 2 i^+k^=-2+0-3r. -1 2 i^+k^=-5r. 2 i^+k^=5

iii We know that the equation r=a+λb+μc represents a plane passing through a point whose position vector is a and parallel to the vectors b and c.Here, a=i^+ j^+0 k^; b=i^+2 j^-k^; c=-i^+ j^-2 k^Normal vector, n=b×c=i^j^k^12-1-11-2=-3 i^+3 j^+3 k^The vector equation of the plane in scalar product form isr. n=a. nr. -3 i^+3 j^+3 k^=i^+ j^+0 k^. -3 i^+3 j^+3 k^r. -3 i^+3 j^+3 k^=-3+3r. 3 -i^+ j^+k^=0r. -i^+ j^+k^=0

iv We know that the equation r=a+λb+μc represents a plane passing through a point whose position vector is a and parallel to the vectors b and c.Here, a=i^- j^+0 k^; b=i^+j^+k^; c=4 i-2 j^+3 k^Normal vector, n=b×c=i^j^k^1114-23=5 i^+j^-6 k^The vector equation of the plane in scalar product form isr. n=a. nr. 5 i^+j^-6 k^=i^- j^+0 k^. 5 i^+j^-6 k^r. 5 i^+j^-6 k^=5-1+0r. 5 i^+j^-6 k^=4r. 5 i^+j^-6 k^=4

Disclaimer: The answer given for part (iv) of this problem in the text book is incorrect.

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