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Determine the number of terms in the arithmetic sequence below:-20, -19, -18, ... 57, 58, 59, 60

User RikiRiocma
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we have the sequence

-20, -19, -18, ... 57, 58, 59, 60​

so

a1=-20

a2=-19

a3=-18

a2-a1=-19-(-20)=1

a3-a2=-18-(-19)=1

the common difference is d=1

Remember the general formula

an=a1+d(n-1)

we have

an=60

a1=-20

d=1

n=?

substitute

60=-20+(1)(n-1)

60+20=n-1

80=n-1

n=81

therefore

the number of terms

User Eric Tobia
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