Question

Using quadratic formula...

Answer 1

\[16a+4b+c=1682\]
\[81a+9b+c=967\]
How do you know if you have to muliply -1 to the top one or to the bottom one?

Answer 2

Trying to find equation 4

Answer 3

to eliminate c

Answer 4

This question is not about quadratic formula.

What you seem to be asking for is how to use the elimination method - correct?

Answer 5

yes

Answer 6

so, in the elimination method we try to eliminate one variable at a time.

as you correctly spotted you can eliminate 'c' by multiplying one of your equations by -1 and then adding the two equations.

it does not matter which one you multiply by -1.

Answer 7

but you wont be able to get the same answer that is why I asked

Answer 8

both will lead to exactly the same answer

Answer 9

you have three unknowns here so I am assuming there is also another equation that you have?

Answer 10

16a+4b+c=1682
49a+7b+c=626
81a+9b+c=967

Answer 11

16a+4b+c=1682 *-1 >-16a-4b-c==1682
49a+7b+c=626
=33a+3b=-1056
This is equation 4
Equation 5 is next sorry my mistake

Answer 12

ok so it doesnt matter if its the top or bottom right?

Answer 13

you should label each equation to help identify them:\[16a+4b+c=1682\tag{1}\]\[49a+7b+c=626\tag{2}\]\[81a+9b+c=967\tag{3}\]So what you have effectively done as your 1st step is (2)-(1) to get:\[33a+3b=-1056\tag{4}\]

Answer 14

correct - it doesn't matter

Answer 15

your next step could be (3)-(1)

Answer 16

ok thanks that is all I needed to know

Answer 17

yw :)