x = y - 5/7
4y - 20/7 + 3y = -34/7
7y = 14/7
y = 2/7
x = 2/7 - 5/7 = -3/7
b) y = 10/21 + x
9x + 20/21 + 2x = -19/7
11x = -57/21 - 20/21
11x = -77/21
x = - 7/21
y = 10/21 - 7/21 = 3/21 = 1/7
lg 3x^2-lg (2x+1)=0
10a^2 -6a+5ab-3b/(5a^2-8a+3)= 5a(2a+b)-3(2a+b)/5a^2-8a+3=(5a-3)(2a+b)/(a-1)(a-3/5)
19*23=437, 19*47=893
НОД(437; 893)=19