Question

Solve the following quadratic equation by completing the square
7x^2+5x+72=3x^2-19x

Answer 1

http://youtu.be/xGOQYTo9AKY

Answer 2

get all the single numbers on the right side...
7x^2 + 5x + 72 = 3x^2 - 19x
7x^2 - 3x^2 + 5x + 19x = -72
combine like terms
4x^2 + 14x = -72

Still with me ?

Answer 3

ok i got you

Answer 4

but 24x instead of 14x right

Answer 5

Now take half of your x, which is 7, and square it. (7 x 7 = 49)
4x^2 + 14x + 49 = -72 + 49
combine like terms
4x^2 + 14x + 49 = - 23

still with me ?

Answer 6

oops...wait...mistake ..hold on

Answer 7

4x^2 + 24x = -72
4x^2 + 24x + 144 = -72 + 144
combine like terms
4x^2 + 24x + 144 = 72

understand so far ? I got the 144 by taking half of coefficient of x (24) which is 12 and then I squared 12 and added to both sides.

Answer 8

yes i understand

Answer 9

Thats it?

Answer 10

no...hold on, this is where I have problems....give me a sec

Answer 11

ok

Answer 12

should divide by four to get the x^2 by itself?

Answer 13

I should have factored....
4x^2 + 24x + 72 = 0
4(x^2 + 6x + 18) = 0

now we have
x^2 + 6x +18 = 0
x^2 + 6x = -18
x^2 + 6x + 9 = -18 + 9
x^2 + 6x + 9 = -9
(x + 3)^2 = -9

I am sorry.....you will need to get better help....I am not good at these....tag someone that can really help you. Again, I am sorry

Answer 14

@satellite73 ...can you help here....I am so not good at these

Answer 15

@hartnn ...can you help...I am not good at this stuff

Answer 16

ok, are we clear till :
get all the single numbers on the right side...
7x^2 + 5x + 72 = 3x^2 - 19x
7x^2 - 3x^2 + 5x + 19x = -72

so, 4x^2 +24x =-72 ?

Answer 17

then divide by 4 throughout to get
x^2+6x = -12
?

Answer 18

i got 18 instead of 12

Answer 19

oops, sorry
x^2+6x =-18\
yes

Answer 20

now step 1 :
divide the co-efficient of x by 2
whats the co-efficient of x here ?

Answer 21

-1/6?

Answer 22

for ax^2+bx=c the co-efficient of x is just "b"
so, here, the co-efficient of x is just 6, got this ?

Answer 23

ok

Answer 24

divide it by 2 , what u get ?

Answer 25

x^2+2x=-9 or does the -18 stay the same

Answer 26

how did u get the 2x ?

Answer 27

i mean 3x

Answer 28

not actually.... i just asked to divide 6 by 2
no modification in original equation yet.
it still stays as x^2+6x = -18

Answer 29

so, since 6/2 = 3, is the step 1 output,
lets got to step 2:
Square it.

so whats 3^2 =...?

Answer 30

9

Answer 31

good, so lets take the original equation now

step 3:
add that to both sides of the equation.

so, what do u get when you add 9 on both sides of
x^2+6x =-18 ?

Answer 32

u still there ?