The first step in designing or redesigning a product is
a. thinking about ways to solve the problem.
b. deciding what needs you are trying to meet.
c. building a prototype.
d. fully researching the problem.

r = ρ x length / area  

ρ = r x area / length  

ρ is in ohm-meters  

in basic units, it is m³kg/s³a²  

i think this is it.

pythagoras' theorem

square root (-5^2+9^2)

square root (25+81)

square root (106)

angle is tan^-1(9/5)

neg x, pos y