Answer:
common difference is 0.5
first term is 5
Step-by-step explanation:
use the formula for the nth term of an ap Tn=a+(n-1)d
T12=10.5
T18=13.5
therefore come up with two equations
T12=a+(12-1)d
10.5=a+11d(1st equation)
T18=a+(18-1)d
13.5=a+17d(2nd equation)
then solve both as a simultaneous equation
a+11d=10.5
a+17d=13.5
-6d/-6=-3/-6
d=0.5
use one of the equations to find the first term
a+11(0.5)=10.5
a+5.5=10.5
a=10.5-5.5
a=5
I hope this helps
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