Question 62

Find k, if the line 4x+y = 1 is perpendicular to the line 5x+ky = 2?

Solution

Slope of line having equation : $$ax + by + c = 0$$ is $$\frac{-a}{b}$$

Thus, slope of line $$4x + y = 1$$ is $$\frac{-4}{1} = -4$$

Similarly, slope of line $$5x + ky = 2$$ is $$\frac{-5}{k}$$

Also, product of slopes of two perpendicular lines is -1

=> $$\frac{-5}{k} \times -4 = -1$$

=> $$\frac{20}{k} = -1$$

=> $$k = -20$$

=> Ans - (B)

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