Lineair calculation part 3 plzz help?

Question

Hi all i wanna say thank u all for myn answers on myn last topic. But iam a bit confused now

This is now easy for me u start by *2
x+y=5
2x+3y=13

and than with *-1 etc......

White this
5x - 6y = 45
3x + 8y = -31
i had some prob in the beginning but

4(5x - 6y = 45)
3(3x + 8y = -31)

20x - 24y = 180
9x + 24y = -93
.......i know the answer now x=3 y=-5

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I cant solve this prob

y=2x+4
y=0.5x-2

Normally u start by * a number in this case i will choose 2* and -1 when i do that and continuing that calculation i will get a weird wrong answer i try d almost everything but cant find any logical answer its so confusing



Its the same with this
y=x^2+3x-4
y=x-1

I cant find anything!!
Can some1 plzz help me!!
Can u also explain it and give me some detail plzz

Thank u very much!!!!!!!!!!!!
when i

Answer 1

x + y = 5
2x + 3y = 13

-2x - 2y = - 10
2x + 3y = 13--------ADD
y = 3
x + y = 5
x = 2
Solution is x = 2 , y = 3

Question 2
5x - 6y = 45
3x + 8y = - 31

40x - 48y = 360
18x + 48y = - 186----ADD
58x = 174
x = 3

9 + 8y = - 31
8y = - 40
y = - 5

Solution is x = 3 , y = - 5

Question 3
2x + 4 = 0.5 x - 2
4x + 8 = x - 4
3x = - 12
x = - 4

y = - 8 + 4
y = - 4
Solution is x = - 4 , y = - 4

Question 4
x² + 3x - 4 = x - 1
x² + 2x - 3 = 0
(x + 3) (x - 1) = 0
x = 1 , x = - 3
Now y = x - 1
Solutions are (1 , 0) , (- 3 , - 4)

Answer 2

well in any simultaneous equations make one of them the subject then substitute to the other equation. but in the y=2x+4
y=0.5x-2
you make: 2x+4=0.5x-2
then gather the like terms on side: 2x-0.5x=-2-4
1.5x=-6
x=-6/1.5
x=-4
then you substitute this answer into one of the y equations
y=2(-4)+4
= -8+4 = -4
there!!
hope it helps