My recent winter holidays were a lot of fun. I tried to visit as many places as I could and to do a lot of different things. Even though the weather wasn't very nice, it didn't make me feel sad. I went to the mall and to the skating-rink with my family and friends. It's always interesting to learn something new, so I also visited the movies and watched some great films. And then, of course, there were New Year and Christmas, which are both my favourite holidays. We had a gorgeous Christmas-tree decorated with toys and Christmas lights. On the first day of new year I got many presents from my family and relatives. After all, it was just great to take some time off from school and to sleep till noon. I really enjoyed my winter holidays.
ответ: при d=-24/5.
Пошаговое объяснение:
Пусть a2, a3, a4, a5 - члены арифметической прогрессии, а d - её разность. По условию, 3*a2+a4=16. А так как a2=a1+d и a4=a1+3*d, то это уравнение можно переписать в виде: 3*a1+3*d+a1+3*d=16, или 4*a1+6*d=16, или 2*a1+3*d=8. И так как a3=a1+2*d и a5=a1+4*d, то P=a3*a5=(a1+2*d)*(a1+4*d)=a1²+6*a1*d+8*d². Из уравнения 2*a1+3*d=8 находим a1=4-3/2*d. Подставляя это выражение в выражение для P, получаем P как функцию аргумента d: P(d)=(4-3/2*d)²+6*(4-3/2*d)*d+8*d²=5/4*d²+12*d+16=5/4*(d+24/5)²-64/5. Отсюда находим d+24/5=0 и d=-24/5.
7:2=3,5 - ширина
3,5+2=5,5 длина