Question 1204943
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You should be careful about the parenthesis placement. 
If in doubt, use a calculator or CAS (computer algebra system) to validate the input.
A rule of thumb: There should be the same number of opening parenthesis "(" compared to the number of closing parenthesis ")". Otherwise things are unbalanced.


It appears you're asking how is (-3/4)(-8a)+(-3/4)(-12) equivalent to both (-3/4)(-8a-12) and 6a+9


The simple answer is <font color=red>distributive property</font>
p(q+r) = p*q + p*r
Multiply the outer 'p' with each term inside.


For example,
2(3+4) = 2*3+2*4 = 6+8 = 14
and using PEMDAS we find that
2(3+4) = 2*(7) = 14
This is one example using numbers to verify the distributive property works. 


Another example
3*(103) 
= 3*(100+3) 
= 3*100 + 3*3
= 300 + 9
= 309
In short, 3*103 = 309


One more example with numbers only
7*(215) 
= 7*(200+10+5) 
= 7*200 + 7*10 + 7*5
= 1400 + 70 + 35
= 1400 + 105
= 1505
In short, 7*215 = 1505


Now let's look at a few examples involving variables
4*(3x+5) = 4*3x + 4*5 = 12x + 20
and
7w*(9w+2) = 7w*9w + 7w*2 = 63w^2 + 14w
and
11(3+6p) = 11*3+11*6p = 33+66p = 66p+33
I encourage you to try other examples on your own.


Why can we extend the distributive property from numbers only to variables? Because variables are placeholders for numbers. It's a more abstract version. 
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