Question

Resolva os seguintes sistemas:
a) x + y = 3
2x + 4y = 4

b) 5x + 7y = 15
4x + 4y = 8

c) -3x + 4y = 15
2x – 5y = -10

Answer 1

a)×+y=3
2×+4y=4
b)5×+7y=15
4×+4y=-10
c)-3×+4y=15
2×-5y=-10

Answer 2

a) x=3-y
2(3-y)+4y=4
6-2y+4y=4
2y=4-6
2y=-2
y=-1

x=3-(-1)
x=4

b) 4x+4y=8 => x+y=2  => x=2-y

5(2-y)+7y=15
10-5y+7y=15
2y=15-10
2y=5

y=5/2

x=2-(5/2) = -1/2

-3x+4y=15 (*2)  = -6x+8y=30
 2x-5y=10  (*3)  =  6x-15y=-30

                                    -7y=0
                                       y=0-7=0

2x-5(0)=-10
2x=-10
x=-10/2=-5