Question

i have two points, (3,5) and (2,18) i need to find the exponential equation using these points. how do i do this?

Answer 1

Answer:  y = (5832/25)*(5/18)^x

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Explanation:

Any general exponential function is of the form

y = a*b^x

Plug in (x,y) = (3,5) and we get

y = a*b^x

5 = a*b^3

If you plug in (x,y) = (2,18), then we'll get this other equation

18 = a*b^2

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So we have this system of equations

$\begin{cases}5 = ab^3\\18 = ab^2\end{cases}$

From here, we divide the two equations straight down. The left hand sides divide to 5/18. The right hand sides divide to (ab^3)/(ab^2) which simplifies to b. The 'a' terms cancel and we subtract the exponents for the b terms.

Overall, we end up with b = 5/18

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Use that value of b to find 'a'

18 = a*b^2

18 = a*(5/18)^2

18 = a*(25/324)

18*(324/25) = a

a = 5832/25

You could use the other equation as well to find 'a'

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Therefore, the equation in y = a*b^x form is y = (5832/25)*(5/18)^x

To verify this, plugging in x = 3 should lead to y = 5. Similarly, plugging in x = 2 should lead to y = 18.