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9.Straight Line
easy
The points $(1, 3)$ and $(5, 1)$ are the opposite vertices of a rectangle. The other two vertices lie on the line $y = 2x + c,$ then the value of c will be
A
$4$
B
$-4$
C
$2$
D
$-2$
(IIT-1981)
Solution

(b) Let $ABCD$ be a rectangle. Given $A\, (1, 3)$ and $C\, (5, 1)$. Equation $B$ and $D$ lie on $y = 2x + c$
We know that intersecting point of diagonal of rectangle is same or at midpoint. So mid point of $AC$ is $(3, 2)$. So $y = 2x + c$ passes throguh $(3, 2)$. Hence $c = – 4$.
Standard 11
Mathematics