中二數學問題

1.
{3x-1=4(y+1)------------------(1)
{7(2x+3)=6y-------------------(2)
From(1) 3x-4y=5-------(3)
From(2) 14x-6y= -21---(4)
(3)*3 9x-12y=15-----(5)
(4)*2 28x-12y= -42---(6)
(5)-(6) -19x=57
x=3

Put x=3 into(3) 9-4y=5
y=1

x=3, y=1
___________________________
2.
{x+9/3-y-10/2=4----------(1)
{x+5y/2=4-------------------(2)
From (1) x+3-y-5=4
x-y=6-----(3)
(2)*2 2x+5y=8-----(4)
(3)*5 5x-5y=6-----(5)
(4)+(5) 7x=14
x=2

put x=2 into(3) 2-y=6
y= -4

x=2, y= -4
____________________________
3A.
{2x+3y=13----------------------(1)
{3x-y=3--------------------------(2)
(2)*3 9x-3y=9-------------(3)
(1)+(3) 11x=22
x=2

Put x=2 into(2) 6-y=3
y=3

x=2, y=3
____________________________
3B.
(a+b)=x=2 and (a-b)=y=3

{a+b=2------------------------(1)
{a-b=3-------------------------(2)
(1)-(2) 2b= -1
b= -0.5

Put b=-0.5 into(1) a-0.5=2
a=2.5

a=2.5, b= -0.5
____________________________


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1. 3x-1=4(y+1) 3x-1=4y+4 3x-4y=5---------------(1)
{ --------->{ --------->
7(2x+3)=6y 14x+21=6y 14x-6y=-21-----------------(2)

(1)x3 9x-12y=15---------------(3)
{
(2)x2 28x-12y=-42------------(4)

(4)-(3):19x=-57
x=3#

x=3代入(1):9-4y=5
-4y=-4
y=1#
ans:x=3,y=1.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2.x+9/3-y-10/2=x+5y/2=4 ---> x-y-2=x+5y/2=4
x-y-2=4 x-y=6--------------(1)
{ --------------->{
x+5y/2=4 2x+5y=8----------(2)

(1)x5 5x-5y=30-------(3)
{
(2)x1 2x+5y=8--------(4)

(3)+(4):7x=38
x=5.4#

x=5.4代入(1):5.4-y=6
y=-0.6#
ans:x=5.4,y=0.6
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
3a. 2x+3y=13------(1)
{
3x-y=3----------(2)

(1)x1 2x+3y=13--------(3)
{
(2)x3 9x-3y=9-----------(4)

(3)+(4):11x=22
x=2#

x=2代入(2):6-y=3
y=3#
ans:x=2,y=3
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
3b. Using the result of (a), solve the simultaneous equations.
2(a+b)+3(a-b)=13 5a-b=13--------(1)
{ ------->{
3(a+b)-(a-b)=3 2a+4b=3--------(2)

(1)x4 20a-4b=52------------(3)
{
(2)x1 2a+4b=3---------------(4)

(3)+(4):22a=55
a=2.5#

a=2.5代入(2):5+4b=3
4b=-2
b=-0.5#
ans:a=2.5,b=0.5
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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1]~using equation one {3x-1=4(y+1)
~chang it to y= which is y= (3x-1over4)1
~then plug y in the second equation 7(2x+3)=6[(3x-1over 4)-1]
~distribute the 7 into the left side of the equation, and the 6 into the right side of the euation to beccome 14x+21=(18x-6 over 24)-6
~subtract 21 on both sides 14x=(18x-6 over24)-27
~spilt all number into fractions 2352x/168=126x/168-(54/168)-27
~solve the last part of the whole equation then gets a decimal of- 26.7, the new equation will be 2352x/168=126x/168-26.7
~multiply 168/126x on both sides of equation it would be (168/126x)*(2352x/168)=.26.7
~solve the left part and it will come out as 296352xsquare=-26.7
~divide both side by 296352
~square root the number and "X" and you will find out what x is.
~plug x into the other formula and solve for y
~you will find what (x,y) is


2.i am sorry i don't understand number 2

3A. use elimination method
~times 3 for the second equation {2x+3y=13 & {9x-3y=9
~eliminate both +3 and -3
~you will get 11x=22
~solve x=2
~plug x into another equation and find out y=3

3B.(a+b)=x=2 and (a-b)=y=3
use substitution and find out a=2.5 b=-0.5