1)
1/x + 3 / (2 2/5 * x) = 3/4
(2 2/5 + 3 ) / (2 2/5 *x) = 3/4
5 2/5 / (2 2/5 * x) = 3/4
2 2/5 * x * 3 = 5 2/5 * 4
(12/5 * 3/1) * x = 27/5 * 4/1
36/5 * x = 108/5
x= 108/5 : 36/5 = (108 * 5) /( 36*5) = 3/1
х = 3 - ответ С. 3
проверим:
1/3 + 3/( 2 2/5 * 3) = 3/4
1/3 + 3/( (12*3)/5) = 3/4
1/3 + 3/1 * 5/36 = 3/4
1/3 + 5/12 = 3/4
4/12 + 5/12 = 3/4
9/12 = 3/4
3/4 = 3/4
2)
1/х - 2/(4 2/3 * х) = 2/7
(4 2/3 - 2) / ( 4 2/3 * х) = 2/7
(2 2/3) / ( 4 2/3 * х ) = 2/7
2 * 4 2/3 * х = 7 * 2 2/3
28/3 * х = 56/3
х = 56/3 : 28/3 = 56/3 * 3/28 = 2/1
х=2 - ответ D. 2
проверим:
1/2 - 2/(4 2/3 * 2 ) = 2/7
1/2 - 2 / ( 14/3 * 2/1) = 2/7
1/2 - 2/1 * 3/28 = 2/7
1/2 - 3/14 = 2/7
7/14 - 3/14 = 2/7
4/14 = 2/7
2/7 = 2/7