# If the straight line $\frac{x}{a} + \frac{y}{b} = 1$ passes through the points (8, - 9) and (12, - 15) find the values of a and b ?

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If the straight line $\frac{x}{a} + \frac{y}{b} = 1$ passes through the points (8, - 9) and (12, - 15) find the values of a and b ?
1. a = 3, b = 2
2. a = 1, b = 5
3. a = 2, b = 3
4. a = 5, b = 1
5. None of these

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Correct Answer - Option 3 : a = 2, b = 3

CONCEPT:

If a line cuts the intercepts a and b on the X and Y – axis respectively, then the equation of such line is given as: $\frac{x}{a} + \frac{y}{b} = 1$

CALCULATION:

Given: The straight line $\frac{x}{a} + \frac{y}{b} = 1$ passes through the points (8, - 9) and (12, - 15)

i.e The points (8, - 9) and (12, - 15) will satisfy the equation $\frac{x}{a} + \frac{y}{b} = 1$

$⇒ \frac{8}{a} - \frac{9}{b} = 1$       -----(1)

$⇒ \frac{12}{a} - \frac{15}{b} = 1$       -----(2)

From equation (1) and (2), we get

$⇒ \frac{8}{a} - \frac{9}{b} = \frac{12}{a} - \frac{15}{b}$

⇒ a = 2b/3       -----(2)

By substituting a = 2b/3 in the equation (1), we get

⇒ $\frac{24}{2b} - \frac{9}{b} = 1$

⇒ b = 3

So by substituting b = 3 in (2), we get

⇒ a = 2

Hence, option C is the correct answer