Explanation:
any linear function represents a straight line (hence the name) and is therefore of the structure
y = f(x) = ax + b
"a" is the slope of the line, and it is represented by the ratio (y coordinate difference / x coordinate difference) when going from one point on the line to another point.
"b" is the y-intercept (the y-value when x = 0).
so, let's look at the answer options :
A.
x = 0 gives us b (the y value) : 2
so, then for x = 1, y = 3 ?
3 = a×1 + 2
a = 1
now, the next point must be also on the same line for the whole function to be linear (and that means the equation has to be true for all numbers involved) :
x = 2, y = 6
6 = 1×2 + 2 = 4
6 is for sure NOT 4, so this is not a linear function.
it is actually y = x² + 2
B.
x = 0 gives us b : 1
for x = 1, y = 3 ?
3 = a×1 + 1
a = 2
again, the next point must be on the same line :
x = 2, y = 9
9 = 2×2 + 1 = 5
9 is for sure NOT 5, so this is not a linear function.
it is actuality y = 3^x.
C.
x = 0 gives us b : 0
for x = 1, y = 1 ?
1 = a×1 + 0 = a
a = 1
the next point :
x = 2, y = 4
4 = 1×2 = 2
4 is for sure NOT 2, so this is not a linear function.
it is actually y = x².
D.
x = 0 gives us b : 3
for x = 1, y = 9
9 = a×1 + 3
a = 6
the next point(s) must fit :
x = 2, y = 15
15 = 6×2 + 3 = 12 + 3 = 15
correct
x = 3, y = 21
21 = 6×3 + 3 = 18 + 3 = 21
correct
yes, this is a linear function.
it is y = 6x + 3