Question

If the straight lines 3x-5y=7 and 4x+ay+9=0 are perpendicular to one another, find the value of a.

Answer 1

3x-5y=7
-5y =-3x+7
y= 3/5x -7/5
so
m¹ = 3/5
4x+ay+9=0
-ay=4x +9
y= -4/ax -9/a
so
m²= -4/a
ATQ
m¹m²=(-1)
3/5(-4/a)=(-1)
12/5 = a

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