I am having trouble with solving these questions using substitution?

Question

y=2x+9

y=7x+10

Answer 1

substitute  qtn 1 to 2

7x+10= 2x+9

7x-2x= 9-10

5x= -1

x= -1/5

solve for y, x= -1/5

y= 2( -1/5) +9

y= -2/5+9

y= (-2+ 5(9))/5

y= 43/5   or 8  3/5

do the checking

Answer 2

Here's a good explanation...

http://www.mathclues.com/MSubstitutionMe...

Hope this helps you!  Please email anytime for further questions.

Answer 3

7x+10 = 2x+9

5x       = -1

x         = -1/5

Answer 4

For substitution, you set one equation equal to one of the unknowns in terms of the others.

Here, both are equal to y.  So take one and substitute it into the other's y:

y = 2x + 9

y = 7x + 10

2x + 9 = 7x + 10

Now solve for x:

-5x = 1

x = -1/5

Now that you have x, plug into either equation and you should get the same y:

y = 2x + 9

y = 2(-1/5) + 9

y = -2/5 + 45/5

y = 43/5

y = 7x + 10

y = 7(-1/5) + 10

y = -7/5 + 50/5

y = 43/5