Decide whether the following sequence is an A.P or not.If so, find the 20th term of the progression: -12,-5,2,9,16,23,30...
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Step-by-step explanation:
t1= -12, t2= -5, t3=2, t4=9
t2-t1=-5-(-12)=-5+12=7
t3-t2=2-(-5)=2+5=7
t4-t3=9-2=7
common difference (d) is constant
it is an A.P
t1=a= -12, n=20, d=7
tn=a+(n-1)d
t20= -12+(20-1)7
t20= -12+(19)7
t20= -12+133
t20=121
20th term is 121
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