2r - 7 = 9
(+7) (+7) >> add 7 to both sides so that only 2r is on that side
2r = 16
2r/2 = 16/2 >> divide both sides by 2 to isolate the variable
r=8 >>16 divided by 2 is 8 which is your answer
3x-y=9 y=3x-9
Solve this problem -x squared -40x- 80 =0
2x-3=9 so 2x=12 and x=6
4
To solve for 2 unknown variables you need 2 independent equations. You have only 1.
9 x 27 equals 243
A + 9 = 21 A = 21 - 9 A = 12
k equals 5.6
.56x=9-.44x x=9
4a - 9 = 27 4a = 36 a = 9
2,2,6,9
3
-9
x=7
10
3x-11 for x=9
D - 9 = 9 d = 9 + 9 d = 18