Предмет: Математика, автор: httpsushi

Проверить свойство возведения в квадрат трехзначных чисел, которые оканчиваются на цифру "5".

Помогите, пожааааалуйста ! Дам 15 баллов !​

Ответы

Автор ответа: M081996
2

Ответ:

Чтобы число, оканчивающееся на 5, возвести в квадрат, можно отбросить последнюю цифру, оставшееся число умножить на число, большее его на один, и приписать справа 25.

Пусть x - число без правой пятерки, тогда можно записать:

(x*10+5)^2 = x^2*100 +2*x*10*5 + 25 = x*(x+1)*100 + 25

Так как любое число если умножить на 100, то у него справа будет два нуля, то решение очевидно: число без 5 умножаешь на число без пяти плюс 1 и приписываешь 25 справа.

httpsushi: Спасибо !!!!
Автор ответа: snenatala45
1

Ответ:

последняя цифра в ответе будет равна 5

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