a) 3x-4y= -1 2x+y= 3 y = 3 - 2x 3x - 4*(3 - 2x) = -1 y = 3 - 2x 3x - 12 + 8x = -1 y = 3 - 2x 11x = 11/:11 y = 3 - 2x x = 1 y = 3 - 2*1 x = 1 y = 1 x= 1 b) 2x+3y= -4 5x+6y= -7 2x = -4 - 3y /:2 5x+6y= -7 x = - 2 - 3/2y 5*(- 2 - 3/2y) + 6y= -7 x = - 2 - 3/2y - 10 - 15/2y + 6y = -7 x = - 2 - 3/2y - 3/2y = 3 /: - 3/2 x = - 2 - 3/2y y = -2 x = - 2 - 3/2* (-2) y = -2 x= -2 + 3 y = -2 x = 1 y = -2 c) 7x+9y= 8 9x-8y= 69 7x = 8 - 9y /:7 9x-8y= 69 x= 8/7 - 9/7y 9* (8/7 - 9/7y) -8y= 69 x= 8/7 - 9/7y 72/7 - 81/7y - 8y = 69 x= 8/7 - 9/7y - 81/7y - 56/7y = 483/7 - 72/7 x= 8/7 - 9/7y - 137/7y = 411/7 / * - 7/137 x= 8/7 - 9/7y y = -3 x= 8/7 -9/7* - 3 y = -3 x = 8/7 + 27/7 y = -3 x = 5 y = -3 d) x/2-y/3= 1/*6 x/4+2y/3= 8 / *12 3x - 2y = 6 3x + 8y = 96 3x = 6 + 2y /: 3 3x + 8y = 96 x = 2 + 2/3y 3*(2 + 2/3y) + 8y = 96 x = 2 + 2/3y 6 + 2y + 8y = 96 x = 2 + 3/2y 10y = 90 x = 2 + 2/3y y = 9 x = 2 + 2/3*9 y = 9 x = 2 + 6 y = 9 x = 8 y = 9 e) x+y/2+2y= 0 / *2 2x + y + 4y = 0 2x = -5y x = -5/2y
