26:
ACB + AB = 360 degrees because circle
(4x + 12) + (x + 13) = 360
5x + 25 = 360
-25 -25
5x = 335
/5 /5
x = 67
27:
x + 2 = y
2x - 1 = y
2x - 1 = x + 2
-x -x
x - 1 = 2
+1 +1
x = 3
plug back into either original equation
x + 2 = y
(3) + 2 = y
y = 5
28: (similar to 27) - the numbers i got are very wonky so I would double check the math
8 = 3x +4y
2x = 5y + 13
taking first equation:
8 = 3x + 4y
-3x -3x
8 - 3x = 4y
/4 /4 /4
2 - 3x/4 = y
then plug that into second equation
2x = 5y + 13
2x = 5(2 - 3x/4) + 15
2x = 10 - 15x/4 + 15
2x = 25 - 15x/4
+15x/4 +15x/4
23x/4 = 25
*4/23 *4/23
x = 100/23
plug this back into either equation and solve for y
2x = 5y + 13
2(100/23) = 5y + 13
200/23 = 5y + 13
-13 -13
-99 = 5y
y = -99/5
This post was edited by Dontrunaway on Apr 1 2016 02:06pm