Предмет: Алгебра, автор: kirilllitovchenko6

4арифметической прогрессии а8=20 a12=10. Найдите а1 и d

Ответы

Автор ответа: sangers1959

Объяснение:

$a_8=20\ \ \ \ a_{12}=10\ \ \ \ a_1=?\ \ \ \ d=?\\\left \{ {{a_8=a_1+7d=20} \atop {a_{12}=a_1+11d=10}} \right. \ \ \ \ \ \left \{ {{a_1+7d=20} \atop {a_1+11d=10}} \right.\ \$

Вычитаем из второго уравнением первое:

$4d=-10\ |:4\\d=-2,5.\\a_1+7*(-2,5)=20\\a_1-17,5=20\\a_1=37,5.$

Ответ: a₁=37,5 d=-2,5.

Предыдущий вопрос

Следующий вопрос

Похожие вопросы

Предмет: Математика, автор: Rufusinda

От леса к озеру побежал муравей со скоростью 3м/мин,а в то же время от озера к лесу поползла улитка со скоростью 6 см/мин. Через 2 часа муравей встретил улитку. Кто из них в этот момент был дальше?

2 года назад

Предмет: Английский язык, автор: nurgaleeva19

Помогите пожалуйста перевести текст "American food and Drink"а то в переводчике неверно!

What is "American" food? The answer is that it is part Italian, part British, part German, part Mexican, part Chinese…When people from other countries came to live in US, they brought different cooking traditions. Some of them opened restaurants. Today Americans enjoy food from all over the world. Over the years some foreign dishes changed a little. Doughnuts were originally from Holland. In 1847 a young American boy told his mother that her doughnuts were never cooked in the middle. He cut out the centres and his mother cooked them — and they were very tasty!
Maybe the US is the most famous for "fast food". The first fast food restaurants served hamburgers, but now they serve other kinds of food too. Inside there is often a "salad bar", where you can help yourself to as much salad as you want.
Americans eat a lot, and when they go to a restaurant, they don't expect to be hungry arterwards. Most restaurants will put a lot of food on your plate — sometimes it can be too much. But if you can't finish it all, don't worry: they will give you a "doggy bag" and you can take it home.
Most Americans now have a light breakfast instead of the traditional eggs, bacon, toast, orange juice and coffee. But on weekends there is more time, and a large late breakfast or early lunch ("brunch") is often eaten with family or friends.

4арифметической прогрессии а8=20 a12=10. Найдите а1 и d ​

Ответы

4арифметической прогрессии а8=20 a12=10. Найдите а1 и d