Answer:
a = 4
Step-by-step explanation:
y = 2x + 1 ......(1)
Going through y - y1 = m(x - x1)
m is slope and it is 2
y1 = 9 and x1 = a
y - 9 = 2(x - a)
y - 9 = 2x - 2a
y = 2x - 2a + 9 ........(2)
Equating (1) and (2)
2x + 1 = 2x - 2a + 9
Collecting like terms
2x - 2x + 2a = 9 - 1
2a = 8
a = 8/2
a = 4
