" Life is not a problem to be solved but a reality to be experienced! "
© Copyright 2013 - 2024 KUDO.TIPS - All rights reserved.
S₃₀ = 90
------------
S₃₀ = (a₁ + a₃₀) * 30/2 = 15(a₁ + 40) = 15a₁ + 600
90 = 15a₁ + 600
15a₁ = 90 - 600 = 510
a₁ = - 510/15 = - 34