The line through A(-2, 3) and B(4, b) is perpendicular to the line 2x - 4y = 5. Find the value of b. [2Marks]
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Solution
Slope of AB =b−34+2=b−36=m1 and 2x−4y=5⇒4y=2x−5 ⇒y=12,c=−54 ∴m2=12 [1Mark]
As the lines are perpendicular, m1m2=−1 ∴m1=−1m2 ⇒b−36=−112 ⇒b−36=−2 b−3=−12⇒b=−9 [1Mark]