ship 2 : x + 4y - 20 = 0 4y = -x + 20 y = -1/4x + 5...slope here is -1/4
so ship 1 has a slope of 4, and ship 2 has a slope of -1/4. These ships are traveling perpendicular to each other because perpendicular lines have negative reciprocal slopes. To find the negative reciprocal of a number, flip the number and change the sign.
so take 4 or 4/1....flip it, making it 1/4....change the sign, making it -1/4. Hence, ur lines have negative reciprocal slopes and are therefore, perpendicular.
