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Find the equation of the line joining A(5,1), B(4,0) using determinants.(a) 4x-y=4(b) x-4y=4(c) x-y=4(d) x-y=0This question was addressed to me in an interview.Question is from Area of a Triangle topic in division Determinants of Mathematics – Class 12

Answer»

Correct option is (c) x-y=4

The best I can EXPLAIN: Let C(x,y) be a point on the line AB. THUS, the points A(5,1), B(4,0), C(x,y) are collinear. HENCE, the area of the triangle formed by these points will be 0.

⇒Δ=\(\frac{1}{2}\begin{Vmatrix}5&1&1\\4&0&1\\x&y&1\end{Vmatrix}\)=0

Applying R1→R1-R2

\(\frac{1}{2}\begin{Vmatrix}1&1&0\\4&0&1\\x&y&1\end{Vmatrix}\)=0

Expanding along R1, we get

=\(\frac{1}{2}\) {1(0-y)-1(4-x)}=0

=\(\frac{1}{2}\) {-y-4+x}=0

⇒x-y=4.



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