I want to ask Maths

1a. 5a-4b+c
b. 7xy+7x-8y
2a. 3x=3
x=1
b. 9-x=7
x=2
c. 4x-3=9
x=3
d. 2x-14=9
x=11.5
e. 2x+3=19
x=8
f. 12/x=4
x=3
g. 10x=10
x=1
h. 11x=7x+16
x=4

(1)(a) 同項放在一起+,-便可以了:a+2b+3c+4a-6b-2c=a+4a+2b-6b+3c-2c=5a-4b+c
(b) 2xy+3x-2y+4x-6y+5xy=7xy+7x-8y
2. solve the following equations for x if m=9,n=2 and l =7.

(a)3x=n+1

3x=? Ans: If n=2, 3x=n+1=2+1, so 3x=3 , so x=1

(b)m-x=l Ans: m-x=9-x=7 ,so x=2

(c)4x-3=m Ans: 4x-3=m=9, so 4x=9+3=12. x=3

(d)2(x-l)=m Ans: 2(x-l)=m=9 , x-1=9/2, so x=9/2+1= 5又2分1

(e) 2x+3=3m-4n Ans: 2x+3=3m-4n=3*9-4*2=19, 2x=19-3=16, so x=8

(f) m+n+1/x=m-l+n Ans: m+n+1/x=m-l+n , 1/x=-7, so x=-1/7

(g) x+2x+3x+4x=m+l-3n Ans: x+2x+3x+4x=10x=m+l-3n, so 10x=9+7-3*2=10, so x=1

(h) 2x+mx=lx+8n Ans: 2x+mx=2x+9x=11x=7x+8*2, so 11x-7x=4x=16, x=4