Q23 of 112 Page 168

The value of k if the straight lines 3x + 6y + 7 = 0 and 2x + ky = 5 are perpendicular is

When the straight lines 3x + 6y + 7 = 0 and 2x + ky = 5 are perpendicular the product of their slopes should be equal to –1 .


Slope of 3x + 6y + 7 = 0 is:


; ()


Slope of 2x + ky = 5 is:



Now we have .


∴ when we substitute the values of m1 and m2 we get:



⇒


⇒ 1 = (–1)×k


⇒ 1 = –k or k = –1

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