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Is the problem (5t - 8) (1 + t)
or
5t - 8 (1 + t)
There is a difference in the parentheses, and I'll tell you why.
Remember PEMDAS? ("Please Excuse My Dear Aunt Sally") This anagram tells you what the order of Operations is.
P - Parentheses
E - Exponents
M - Multiplication
D - Division
A - Addition
S - Subtraction
Do each of these in order, and that's how arithmetic works.
Now, back to your problem. I believe it should be
(5t - 8) (1 + t)
The distributive property says that you can multiply each monomial in a parentheses separately by a common monomial. What this means is that you can do exactly what is written down in your post. You multiply the first number on the left side, which in this case is 5t, by the first number on the right. Then multiply the first number on the left side with the second number on the right side, which would make 5t * t. Do the same for the next number, 8. If you expand this, it becomes:
5t(1) + 5t(t) - 8(1) - 8(t)
5t + 5t2 - 8 - 8t
5t2 - 3t - 8
That is the expanded version of your problem. I hope that makes sense. Remember that the distributive property only applies when you are multiplying a parentheses by some number (or in this case, another set of parentheses). Also remember your signs! ( + and - )