Question

Vector Analysis : Find a vector equation for the line through (1,2) perpendicular to the line with vector equation r=7i+2j+t(3i+4j).

Answer 1

your line would be
r = 1i + 2j + t(xi + yj)
again you have
x*3 + 4 *y = 0
you would get, 3x = -4y
hence you line would be
t(3xi+3yj) = -4y i +3yj = y(-4i+3j)

so you line is i+2j+t(-4i+3j)

Answer 2

thanks @experimentX