1) (2/5)³ = 8/125
2) -(-3/7)² = - 21/49
3) -4² <span>+ (-6) = 16 - 6 = 10
</span>4) (-0,3)⁴ <span>- (-0,2)</span>² = 0,0081 - 0,04 = -0,0319
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Sₙ = n(2a₁+d(n-1)) / 2
S₁₅ - S₁₄ = 15(2a₁+14d) / 2 - 14(2a₁+13d) / 2 = 87
2a₁+ 14(15-13)d = 87*2
a₁ + 14d = 87
S₁₁ - S₁₀ = 11(2a₁+10d) / 2 - 10(2a₁+ 9d) / 2 = 43
2a₁ + 10(11-9)d = 43*2
a₁ + 10d = 43
14d - 10d = 87 - 43 = 44
d = 11