Bradford T. answered 12/11/20
Retired Engineer / Upper level math instructor
When multiplying polynomial like this, the common method is call the FOIL method.
It stands for First, Outer, Inner,Last:
For example
(a+b)(c+d) = ac + ad + bc + bd
a and d are the Outers and b andc are the Inners.
Where a is the first term to be distributed through the second part.
If it was only something like
a(c+d)
then you would distribute a through (c+d) giving ac + ad. Remember the rule for multiplication over addition.
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Another way to look at it is:
(a+b)(c+d) is the same as a(c+d) + b(c+d).
For this case 3x is a, b is 4, c is x and 2 is d.
So it would be 3x(x+2) + 4(x+2) = 3x2+6x + 4x + 8. 6x and 4x can be combined to make 10x.
The final answer is 3x2+10x+8