Question

R=-3s-1/4. r+3s=20
Como puedo resolver esta ecuacion???

Answer 1

r = 3s - 1/4
r+3s = 20 ⇒  r = -3s +20

si sumamos las dos igualdades de r nos queda así:
 r =  3s - 1/4
 r = -3s + 20
2r = 0s + (20 - 1/4)
2r = (80/4) - (1/4)
2r = 79/4
r = (79/4) / 2
r = 79 / (4*2)
r = 79/8

r + 3s = 20
79/8 + 3s = 20
3s = 20 - 79/8
3s = (160/8) - (79/8)
3s = 81/8
s = (81/8) / 3
s = 81 / (8*3)
s = 81/24
s = 27/8

Comprobación:
r = 3s - 1/4
79/8 = (3*27/8) - 1/4
79/8 = 81/8 - (2/8) 

Respuesta:
r = 79/8
s = 27/8

Answer 2

Tenemos un sistema de ecuaciones

         r = - 3s - 1/4     (I)
         r + 3s = 20       (II)
De (2)
             r = 20 - 3s    (III)
(I) = (III)
    r = r
Entonces
                      - 3s - 14 = 20 - 3s
                      - 3s + 3s = 20 + 1/4
                       0 = 20 + 14 ????????? IMPOSIBLE

                                        SISTEMA IMPOSIBLE