Question

show that straight lines 2x+y=5 and x-2y=4 are at right angles

Answer 1

First find out the slopes of the lines .

2x+y=5
y=5-2x this is in the y=Mx+c form
The slope is -2.

x-2y=4
y=X/2 -2
The slope is 1/2.

For the lines to be perpendicular the product of the slopes is equal to -1.
1/2 × -2 = -1
Therefore the two line are at right angles.