exponential fcns: find eqn, given (0, -2), (2, -50) on curve

[Jen123]

Use the equation of the exponential function whose graph passes through the points (0, -2) and (2, -50) to find the value of y when x=-2.

I came up with 50, but I got the question wrong, and now I'm confused about the process.

 

[mmm4444bot]

Please Give Us A Clue.

Hi Jen123:

Will you please post your process, so that we can see why you ended up with 50?

This will help us greatly to understand where you went wrong.

~ Mark

Oh, btw, please also confirm the base in your exponential function.

The exponential function with base 'a' is: y = a^x.

The natural exponential function has base e: y = e^x.

Thanks

 

[Jen123]

I used the exponential function y = ab^x. I subtracted x_2 - x_1:

. . .2 - 0 = 2

So x = 2. I plugged the coordinates into this equation:

. . .-50 = -2b^2

. . .25 = b^2

Instead of dividing, I multiplied and put b = 50.

 

[stapel]

I used the exponential function y = ab^x. I subtracted...

I'm sorry, but I can't make heads or tails of what you're doing...?

Try using the standard exponential formula, y = ab^x, and plug in the points to solve for "a" and "b".

. . . . .(x, y) = (0, -2):

. . . . .y = ab^x
. . . . .-2 = ab⁰
. . . . .-2 = a(1)
. . . . .-2 = a

This gives you the value of "a". Now plug in the other point and solve for the value of "b".

Note: Since 50² = 2500, not 25, then "b" can not possibly be 50.

Eliz.