Question 179895
9x+4y=1
4y=-9x+1
y=-9/4x+1/4

The slope of this line is -9/4

4x-9y=3
9y=4x-3
y=4/9x-1/3

The slope of this line is 4/9.

-9/4 and 4/9 are negative reciprocals. Therefore, the lines are perpendicular.

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