A farmer wants to fence a rectangular area of 12km2 and then divide it in half with a fence parallel to one of its sides of the rectangle find the dimensions of the rectangle that will minimize the amount of fencing used

Can someone explain the elimination method to me for this problem?

Acable company wants to provide cell phone service for residents on an island. the function for the cost of laying the cable from the island to the mainland is c(x)= 6.500 square root x2+4, where x represents the length of the cable in feet. what are the domain and range of the function? a) domain: all real numbers range: all real numbers greater than or equal to 17,000 b) domain: all real numbers greater than or equal to 0 range: all real numbers greater than or equal to 17,000 c) domain: all real numbers greater than or equal to 0 range: all real numbers greater than or equal to 13,000 d) domain: all real numbers greater than or equal to 13,000 range: all real numbers greater than or equal to 0

What is the vertex form of f(x) = x2 + 6x + 3