Question

dado a p.a (-2,-4...) determine:
a) A16
b) A20=50
c) A10=30
d) A20

Answer 1

r = a2 - a1
r = -4-(-2)
r = -4+2
r = -2

a)
an = a₁ + ( n -1 ). r
a₁₆= -2 + (16-1).(-2)
a₁₆ = -2+( - 32 +2)
a₁₆ = -2+(-30)
a₁₆ = -2 - 30
a₁₆ = -32

d)
a₂₀= -2 + (20-1).(-2)
a₂₀ = -2+( - 40 +2)
a₂₀= -2+(-38)
a₂₀ = -2 - 38
a₂₀ = -40