Răspuns:
Explicație pas cu pas:
a) 6/8 =3/y, 6y = 3*8, y = 24/6 = 4
b) (x+1)/15 =2/3
3(x+1) = 2*15, 3x +3 = 30, 3x = 27, x = 9
c) (7x+21)/(x+2) = (x+3)/5
5(7x+21) = (x+3)(x+2)
35x +105 = x^2 +5x +6
x^2 -30x -99 = 0
delta = 900 - 396 = 504= 36*14
x1,2 = (30 -+6√14)/2
x1 = (30 -6√14)/2 = 15 -3√14
x2 = (30 +6√14)/2 = 15 +3√14