Straight LineHardBloom L3

Question

If $m$ and $b$ are real numbers and $mb > 0$, then the line whose equation is $y = mx + b$ cannot contain the point:

Options

A.$(0,2008)$
B.$(2008,0)$
C.$(0, - 2008)$
D.$(20, - 100)$

Solution

Sol. [Key Concept: A line $y = mx + b$ through $(x_{0,0)}$ gives $mb = - m^{2}x_{0}$; with $mb > 0$ a point with positive $x$-intercept cannot lie on it.]

$$mb > 0 \Rightarrow m > 0 $$and $b > 0$ or $m < 0$ and $b < 0$

Hence possible lines are as shown

In both the cases $x$ intercept cannot be +ve

⇒ (b)

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