Answer:
The first term will be 38.375
Explanation:
aₙ = a₁ + (n - 1) * d
a₂₀ = -40
a₂₈ = -73
-40 = a₁ + 19d
-73 = a₁ + 27d
When we have two similar equations with two unknowns, we can subtract them to get an answer.
-40 = a₁ + 19d --> -40 = a₁ + 19d
-(-73 = a₁ + 27d) --> 73 = -a₁ - 27d
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33 = -8d
Solve for d by dividing by -8
d = -4.125
Now plug d into one of the original equations to solve for a₁
-40 = a₁ + 19(-4.125)
-40 = a₁ - 78.375
a₁ = 38.375