Step-by-step explanation:
when multiplied together, the gradients of the 2 graphs should equal -1 (of they are perpendicular).
x-7y=4
-7y= -x + 4
y= -1/7 x + 4/7
21x+ 3y=11
3y=-21x+11
y=-21/3 x + 11/3
-21/3 * -1/7 = 1
when multipled together, the 2 gradients dont equal -1 therefore they are not perpendicular
unless I've made a mistake with the signs at some point haha
