algerbra questions !!! help?

Question

plz show step by step how to do thx


the proportion x+4/3 = 7/x has the solution or solutions?


the LCM of 8ab and 12a^2 is?


the rational expression 5x/x^2-9 is undifined only when x=what?


if two variables are related inversly then as one variable dereases,the other variable does what?


in the proportion 3/x=7/x+4 the cross the production are?

Answer 1

1.(x+4)/3=7/x
=>x^2+4x=21
=>x^2+4x-21=0
=>(x+7)(x-3)=0
Therefore x= -7 or 3
2.It will be 24a^2b
3..When x^2-9 is undefined
4.When two variables are related inversely,their product is constant.So if one variable decreases,the other increases.
5.3/x=7/(x+4)
The products on cross multiplication are 7x=3x+12

Answer 2

x^3 + 4x = 21
x^3 + 4x - 21 = 0
factors easily and has 2 solutions

2^3ab, 3*2^2a^2b
LCM = 3*2^3a^2b

5x/x^2-9
This expression is undefined when x^2 - 9 = 0, so there are 2 values of x for which it is undefined.

if two variables are related inversly then as one variable dereases,the other variable does what?
..the inverse of decreasing

in the proportion 3/x=7/x+4 the cross the production are?
3(x + 4) = 7x