JEE Advanced · Mathematics · 9. Straight Lines

For a > b > c > 0, the distance between (1, 1) and the point of intersection of the lines ax + by + c = 0 and bx + ay + c = 0 is less than $2 \sqrt{2}$ .Then

A $a + b - c > 0$
B $a - b + c < 0$
C $a - b + c > 0$
D $a + b - c < 0$

Verified Solution

Answer & Solution

Correct Answer

(A) $a + b - c > 0$

Step-by-step Solution

Detailed explanation

(a - b) x + (b - a) y = 0

\Rightarrow x = y

\Rightarrow Point of intersection (\frac{- c}{a + b}, \frac{- c}{a + b})

Now using distance formula between two points

d = \sqrt{{(x_{1} - x_{2})}^{2} + {(y_{1} - y_{2})}^{2}}

\Rightarrow \sqrt{{(1 + \frac{c}{a + b})}^{2} + {(1 + \frac{c}{a + b})}^{2}} < 2 \sqrt{2}

\Rightarrow \sqrt{2} (|\frac{a + b + c}{a + b}|) < 2 \sqrt{2}

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

Same subject

	List- $I$		List- II
$(I)$	$2 h + k$	$(P)$	$6$
$(I I)$	$\frac{L e n g t h o f Z W}{L e n g t h o f X Y}$	$(Q)$	$\sqrt{6}$
$(I I I)$	$\frac{A r e a o f t r i a n g l e M Z N}{A r e a o f t r i a n g l e Z M W}$	$(R)$	$\frac{5}{4}$
$(I V)$	$α$	$(S)$	$\frac{21}{5}$
		$(T)$	$2 \sqrt{6}$
		$(U)$	$\frac{10}{3}$

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For a > b > c > 0, the distance between (1, 1) and the point of intersection of the lines ax + by + c = 0 and bx + ay + c = 0 is less than 2 2 .Then

Step-by-step Solution

For a > b > c > 0, the distance between (1, 1) and the point of intersection of the lines ax + by + c = 0 and bx + ay + c = 0 is less than $2 \sqrt{2}$ .Then