Three numbers $a , 0 , b$ form an arithmetic sequence in this order, and three numbers $2 b , a , - 7$ form a geometric sequence in this order. What is the value of $a$? [3 points] (1) 10 (2) 12 (3) 14 (4) 16 (5) 18
Three numbers $a , 0 , b$ form an arithmetic sequence in this order, and three numbers $2 b , a , - 7$ form a geometric sequence in this order. What is the value of $a$? [3 points]\\
(1) 10\\
(2) 12\\
(3) 14\\
(4) 16\\
(5) 18