A₂=10 d=-2 S=-558 n-? >0
a₂=a₁+d=a₁+(-2)=10
a₁=12
S=(2*a₁+(n-1)*d)*n/2
(2*12+(n-1)*(-2))*n/2=-558 |×2
(24-2n+2)*n=1116
(26-2n)*n=1116
26n-2n²=1116 |÷(-2)
n²-13n-558=0 D=2401 √D=49
n₁=31 n₂=-18 ∉.
Ответ: n=31.
1) 5⁷ * 5⁻² = 5⁷⁻² = 5⁵ = 3125
2) 10⁹ : 10⁰ = 1 000 000 000 : 1= 1 000 000 000
![3)\frac{7^{-3}*7^{-4}}{7^{-8}}=7^{-3-4-(-8)}=7](https://tex.z-dn.net/?f=3%29%5Cfrac%7B7%5E%7B-3%7D%2A7%5E%7B-4%7D%7D%7B7%5E%7B-8%7D%7D%3D7%5E%7B-3-4-%28-8%29%7D%3D7)
4)16 * 2⁻⁶ = 2⁴ * 2⁻⁶ = 2⁻² = 0,25
5) 2b⁴ - b² = b²(2b² - 1)
6) 25b⁸ - 4a² = (5b⁴)² - (2a)² = (5b⁴ - 2a)(5b⁴ + 2a)
2х+3у=60. 2(30+у)+3у=60
х=30+у. 60+2у+3у=60
5у=0
у=0
х=30
Ответ: (30;0)
<em>24 + x = 0.6x + 7.4;</em>
<em>x - 0.6x = 7.4 - 24 ;</em>
<em>-0.4x = 16.6;</em>
<em>x = -41.5 ;</em>
<em>Проверка :</em>
<em>24 +(- 41.5) = 0.6 * (-41.5) +7.4 ;</em>
<em>-17.5 = -17.5 ;</em>
<u><em>Обращайся)</em></u>