Will mark as what is the determinant of the coefficient matrix of this system?

2x + 3y + z = 19
x + z = 6
x + 2y - z = 8

1. what are the missing reasons in the proof 2. it's in the second picture and 3

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

Which polynomial function has x intercepts -1, 0, and 2 and passes through the point (1, -6)