please tell me if i did my trig work right.

[leesuh190]

find the equation of the parabola, y=ax^2+bx+c, that passes through (1,1), (-1,11) and (3,23).
my work:
1=a+b+c
11=a-b+c
23=9a+3b+c

so then i multiplied the second equation by -1 and annd added the 1st and 2nd equations together and did the the same thing with the third equation and added 1st and 3rd equation.

and i got

1=a+b+c
b=-5
a=22/8
c=17/4

did i do it right?
_____________________________________________________________

a total of $11000 is invested in 2 funds paying 7% and 8% simple intrest. if the yearly interest for both funds totals $865, determine the amount invested at 8%.
my work:
so i made 2 equations

x+y=11000
.07x + .08y=865

and by usuing substitution i got that x=1500 and y=9500. am i right?

 

[Denis]

1=a+b+c
b=-5
a=22/8
c=17/4
did i do it right?

NO. 22/8 - 5 + 17/4 is not equal to 1.
b = -5 is correct.

...and by usuing substitution i got that x=1500 and y=9500. am i right?

YES. Good job :idea:

 

[galactus]

find the equation of the parabola, y=ax^2+bx+c, that passes through (1,1), (-1,11) and (3,23).
my work:
1=a+b+c
11=a-b+c
23=9a+3b+c

so then i multiplied the second equation by -1 and annd added the 1st and 2nd equations together and did the the same thing with the third equation and added 1st and 3rd equation.

and i got

1=a+b+c
b=-5
a=22/8
c=17/4

did i do it right?

You have the right idea, but I think you strayed somewhere.

Your system of equations is correct. If you solve it you should get:

a=4, b=-5, c=2
_____________________________________________________________

a total of $11000 is invested in 2 funds paying 7% and 8% simple intrest. if the yearly interest for both funds totals $865, determine the amount invested at 8%.
my work:
so i made 2 equations

x+y=11000
.07x + .08y=865

and by usuing substitution i got that x=1500 and y=9500. am i right?

You are correct. You can set it up as \(\displaystyle 0.07x+0.08(11000-x)=865\)

You did good. You just set up up another way.