Question

Find k, if the line 4x - y = 1 is perpendicular to the line 5x - ky = 2?<br /><br />Options:<br /><br />1) 20<br /><br />2) -20<br /><br />3) 4<br /><br />4) -4<br /><br />

Answer 1

4x - y = 1

y = 4x +1

Slope (m1) = 4

5x- ky =2

ky = 5x +2

y = (5/k)x +2/k

Slope (m2) = 5/k

Both line are perpendicular, so

m1×m2 = -1

4×(5/k) = -1

k = -20

Option no . (2) -20

Hope it helps