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