-1=1/2a+9
move +9 to the other side
sign changes from +9 to -9
-1-9=1/2a+9-9
-1-9= 1/2a
-10= 1/2a
Mutiply both sides by 2/1
(-10)(2/1)= 1/2a*2/1
Cross out 2 and 2, divide by 2 and becomes 1
Cross out 3 and 3 , divide by 3 and becomes 1
1*1*a= a
a= -20
Answer: a= -20
