Задание
20 20
----- + ----- =7
x+y x-y
2 5
---- = ---
x-y x+y
Решение
20(x-y)+20(x+y)=7(x-y)(x+y)
2(x+y)=5(x-y)
20x-20y+20x+20y=7(x²-y²)
2x+2y=5x-5y
40x=7x²-7y²
3x=7y y=3x/7
40x=7x²-7 * 9x²/49
40x=7x²-9x²/7
40x*7=7x² *7 - 9x²
280x=49x²-9x²
280x=40x² (делим на 40х)
7=x
y=3x/7 = 3*7/7 = 3
Ответ : (7:3)