<span>(x−1)^2 / x^2+4x−5
2х-2/2х+4х-5
2х-2/6х-5</span>
Решение
<span>a</span>₂ <span>= a</span>₁ <span>+ d
</span><span>a₉ </span><span>=a₁ </span><span>+ </span><span>8d
</span><span>a</span>₂ <span>= 3a</span>₉
<span>3(a</span>₁ <span>+ 8d) = a</span>₁ <span>+ d
</span><span>3a</span>₁ <span>+ 24d = a</span>₁ <span>+ d
</span><span>2a</span>₁ <span>+ 23d = 0
</span><span>2a</span>₁ = - 23d
<span>a</span>₁ = - 11,5d
<span>Sn = [2a</span>₁ + d*(n - 1)*n]/2
S₂₀ = [(a₁ + a₁ + 19d)*20]/2 = (a₁ + a₂₀)*10
<span>
</span>
0.2х+0.3у=1.2 умножим на 2
0.5х-0.6у=0.3
0.4х+0.6у=2.4
0.5х-0.6у=0.3 сложим
0.4х+0.5х=2.4+0.3
0.9х=2.7
х=3 подставим в первое
0.2*3+0.3у=1.2
0.6+0.3у=1.2
0.3у=1.2-0.6
0.3у=0.6
у=2
Ответ:
х=3
у=2