Question

What happens to the value of the expression 80 - 2r as r decreases?

Answer 1

Answer:

(80-2r)-r

- , - = +

so, (80-3r) is right answer

Answer 2

Answer:

(80-2r)- r

-80r+2r^2

2r^2-80r=0

r=-+100

$= + - ( - 80) + \sqrt{( - 80) - 4 \times 2 \times 1 } \div 2 \times 2 \\ = - + 80 + \sqrt{6400 - 8} \div 4 \\ = - + 20 + 80 \\ = - + 100$