Question

Find the minimum value for the function: y = x^2 + 9x + 18

Answer 1

do u knwo how to complete the square? or do u factor it?

Answer 2

lets factor its easy

Answer 3

its under my quadratic function lesson so idk

Answer 4

what 2 numbers when you multiply them =18 and when u add them =9?

Answer 5

is there a number for that?

Answer 6

6*3=18
6+3=9

Answer 7

ohhh

Answer 8

so is the answer 9
?

Answer 9

yaaaa factoring i just taught this to my class today.
hmmmm nooooo we r factoring. We r trying to figure out 2 numbers that when u mulyiply them give us 18 and when u add them gives us 9

Answer 10

finding the zeros is a long and complicated way to find the minimum

Answer 11

umm well we can complete the square

Answer 12

but i dont think she knows that

Answer 13

use the vertex formula

Answer 14

minimum is at the vertex, and first coordinate of the vertex of
\[y=ax^2+bx+c\] is always \(-\frac{b}{2a}\)

Answer 15

when doing the vertx thing... is the second number the minimum?

Answer 16

in your case it is \(-\frac{9}{2}\) replace \(x\) by \(-\frac{9}{2}\) to find the minimum

Answer 17

minimum means minimum value of \(y\) so it is the second coordinate, not the first

Answer 18

so yes, what you said, the second number is the minimum.

Answer 19

ohhh i like this method. We never learnt this stuff. Like the textbook always made us complete the square. oh cooll

Answer 20

can i just plug it into my graphing calculator to get the anwser ?

Answer 21

completing the square is for suckers, unless of course you are solving a quadratic equation

Answer 22

last i heard minimum value was in a calculus class o.O i never knew it was in algebra too

Answer 23

It's in Algebra 2.

Answer 24

You can use a calculator to solve it

Answer 25

hahah its in math 11 here in canada

Answer 26

\[(-\frac{9}{2})^2+9\times (\frac{-9}{2})+18\] then a calculator if you need one

Answer 27

you turn math up to eleven in canada? mine only goes up to ten

Answer 28

Ti-84, input the equation into Y= then click 2nd Trace, and do minimum. It will say "Left bound?", go to the left side of the graph and press enter. Right bound? Obviously, right side. It will say "Guess?", which means put it to where you think the minimum y value is.

Answer 29

So for this, you get x=-4.5 and y=-2.25

Answer 30

sooo many numbers ... ahhhhh!!! >_< what about TI-83 plus?

Answer 31

hahaha grade 11 math lol

Answer 32

so taking the derivative and equating to zero is another story?

Answer 33

It'll be exactly the same basically I think.

Answer 34

Yes lgb haha

Answer 35

they give us this freshman yr. imma senior now tryna make it up.. sucks :/

Answer 36

thanks everyone

Answer 37

using the derivative to find the minimum value of a quadratic. like using a glock to kill a wingspanroach