Я думаю так)))))))))))))))
Решение
<span>S</span>₅ <span>= 1/2(a</span>₁ <span>+ a</span>₅<span>)•5 = 1/2(a</span>₁ <span>+ a</span>₁ <span>+ 4d)•5 = (a</span>₁ <span>+ 2d)•5
</span><span>S</span>₆₋₁₀ <span>= 1/2(a</span>₆ <span>+ a</span>₁₀<span>)•5 = 1/2(a</span>₁ <span>+ 5d + a</span>₁ <span>+ 9d)•5 = (a</span>₁ <span>+ 7d)•5
</span><span>Найдём разность этих сумм, она равна 200
</span><span>5(a</span>₁ <span>+ 2d) - 5(a</span>₁ <span>+ 7d) = 200</span><span>a</span>₁ <span>+ 2d - a</span>₁ <span>- 7d = 40
</span><span>- 5d = 40
</span><span>d = - 8
</span><span>Аналогично найдём разность суммы с 1 по 10 и с 11 по 20
</span><span>10•1/2(а</span>₁ <span>+ а</span>₁₀<span>) - 10•1/2(а</span>₁₁ <span>+ а</span>₂₀<span>) =
</span><span>= 5(a</span>₁ <span>+ a</span>₁ <span>+ 9d) - 5(a</span>₁ <span>+ 10d + a</span>₁ <span>+ 19d) = 5(9d - 29d) =
= 5(- 20d) =</span><span> 5(- 20)*(- 8) = 800
</span><span>Ответ: 800</span>
7/10х+14/5=(3/5х-18/5)+8.7
7/10х+14/5=3/5х+51/10
нок 10
7/10х+14/5=3/5х+51/10 |*10
7х+28=6х+51
х=23
/ дробь
|* значит умножаем уравнение на 10
надеюсь поймешь
(a+ b)/8c³ * 16c³/(a+b) =2
(m+n)/(m-n) : 3m/(m-n)=(m+n)/(m-n) * (m-n)/3m=(m+n)/3m
(x+y)/(x-1) : (y-2)(/(4x- 4)=(x+y)/(x-1) * (4(x-1))/(y-2)=4(x+y) / (y-2)
(5n-5m)/(3(a+2)) * (2a²+a³)/(n-m)=(5(n-m))/(3(a+2)) * (a²(2+a))/(n-m)=5a²/3
.
(7a+7b)/5c² * 14c/(6b+6a)=(7(a+b))/5c² * 14c/(6(b+a))=21/30c=7/10 c
при с=3,5
7*3,5/10=24,5 : 10=2,45
(b-5)/(4-4c) : (b² -25)/(c-c²)=(b-5)/(4(1-c)) * (c(1-c))/((b-5)(b+5))=c/(4(b+5))
при b=2, c= -35
- 35/(4(2+5))= - 35/28= - 5/4= - 1.25
