suatu fungsi f(x) = 4x + 1; f(a) = -9 dan f(2) = b. nilai dari a-b adalah... (tolong yaa kasih caranya sekalian)

f(a)= -9

=> 4a+1= -9
=> 4a= -9-1
=> 4a= -10
=> a= -10÷4
=> a= 2,5

f(2)= b

=> 4(2)+1
=> 8+1
=> 9

a-b
=> 2,5-9
=> -6,5

f(a) = -9
4a + 1 = -9g
4a = -9 -1
4a = -10
a = -10/4
a = -5/2 atau -2,5

f(2) = b
4(2) + 1 = b
8 + 1 = b
9 = b
b = 9

jadi
a - b = -5/2 - 9
= -5/2 -18/2
= - 23/2

atau

a-b = -2,5 - 9
= -11,5