math help please????

Question

2x-7y=3
and x=1-4y


every time i get the answer 3 or 1/-15
and my math teacher said it's wrong

gahh!
my teacher told my friend that the answer is -5
but i have to show work!

Answer 1

sorry.. i got the same answer:
2x-7y=3
2(1-4y)-7y=3
2-8y-7y=3
2-15y=3
-15y=3-2
-15y=1
divide both sides by -15
-15y/-15=1/-15
y=1/-15

BUT i tried solving it using x instead of y, so i transposed the x=1-4y into 4y=1-x, which results in y = (1-x)/4
using that, here's my solution:
2x-7y=3
2x-7((1-x)/4)=3
if i multiply 7 to 1 & x, i get (7-7x)/4
2x- (7-7x)/4=3
then, i treat 2x as a fraction, which is 2x/1
so,
2x/1 - (7-7x)/4 =3
then, i subtract the two fractions using 4 as the lcd
(8x-7+7x)/4=3
simplify it:
(15x-7)/4=3
separate x and 7
15x/4 - 7/4=3
15x/4= 3+7/4
then, i add 3 and 7/4 using 4 as the lcd again:
15x/4=(7+12)/4
15x/4=19/4
then i cross multiply:
60x=19*4
60x=76
then i divide both sides by 60
60x/60=76/60
x=76/60 or 1.27(rounded up)

check it using the formula i used: 2x-7((1-x)/4)=3
it returns approx. 3

hope it's right! ^__^

Answer 2

Your teacher is wrong. Tell her BOB(Back Of Book) is wrong, and to work it out him/herself.



Substitute 1-4y for x

2(1-4y)-7y=3
multiply out

2-8y-7y=3
combine like terms

2-15y=3
-2 -2
-15y=1
/-15 /-15

y= -1/15

Now plug into an equation and solve for x

x=1-4(-1/15)
x=1-(-4/15)
x=1+ 4/15 or 19/15

check your answers

19/15=1-4(-1/15)
19/15=1-(-4/15)
19/15=1+ 4/15
correct

your answer is x=19/15 and y=-1/15
OR
your answer is (19/15, -1/15)

Answer 3

2x-7y=3

2(1-4y)-7y
distributive property.
2 times 1 plus 2 times 4y.equals.2+8y-7y=2+1y

2+1y is the answer i believe

Answer 4

The answer is: x=19/15 and y= -1/15

Answer 5

2(1 - 4y) -7y = 3
2 -8y -7y = 3
-15y = 1
y = -1/15

Are these the two original equations?

Answer 6

solve for y first

add 7y to both sides of the top equation, you should get that 2x=7y+3

then divide both sides of that equation by 2, you should get x=3.5y+1.5

then combine the right sides of the two equations (since the right sides of both are equivalent to x) you should get that 3.5y+1.5=1-4y

after that you solve as you would any other equation

3.5y+1.5=1-4y add 4y, subtract 1.5
7.5y=-.5
y= -0.066666666666666666666666...

unusual answer, you should make sure the equations are correct

then solve for x

x=1-4(-0.06666666666666666...) substitute -.066666... for y into one of the equations

x=1+0.266666666666... multiply

x=1.26666666666666.... add (two negative signs next to each other mean to add)

hope this helps

Answer 7

I get x = 19/15 and y = -1/15.

Answer 8

2(1-4y)-7y=3
2-8y-7y=3
2-15y=3
-15y=1
y= -1/15

x=1-4y
x=1-4(-1/15)
x=1+4/15

the answers are -1/15 and 1+4/15

Answer 9

y=(-3/7)+(-2/7)X(answer to 2X-7y=3)
y=(1/4)-(X/4)(answer to x=1-4y)