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(-3/4)³ + 3³/4 - 3/(-4)³ = приводим к общему знаменателю и выносим одинаковые члены
-3³/4³ + 3³4²/4³ + 3/4³ = 3/4³*(-3² + 3²4² + 1) = 3/4³*(-9 + 144 + 1) = 3*136/4³= 3*34/4² = 102/16 = 51/8 = 6 3/8
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An = A1 + (n - 1)D;
A1 = An - (n - 1)D;
A1 = 38 - (15 - 1)*3 = 38 - 14*3 = 38 - 42 = -4;
Sn = n*(2A1 + D(n-1))/2
S10 = 10*(2*(-4) + 3(10-1))/2 = 10*(-8 + 27)/2 = 5*19 = 95;