The original expression evaluates to 54.4 as shown in the first working.
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For some reason, 3.4 got transcribed to be 1.7 in the 3rd line of the second working. There is no math operation in the expression that requires 3.4 to be divided by 2.
The whole length of the poster is 4 feet. There are three people who will paint an equal length, so this means that we need to divide the 4 feet of the poster between 3 people.
4 ÷ 3 <span>≈ 1.3
Each student will paint 1.3 feet, or 1 foot and 4 inches of the poster.</span>
(0.4+0.75)/0.5
Your answer is 2.3
UPDATE
the answer is either 2 (3/10) as a mixed number or 23/10 as an improper fraction
For quadratics, these formulas are used mainly for factoring.
Your equation can be written as ...
... 2(x² +2x -3) = 0
You factor this by looking for factors of -3 (c=x1·x2) that add to give +2 (b=-(x1+x2)). These are {-1, +3}, so the factorization is ...
... 2(x -1)(x +3) = 0
The roots are then 1 and -3, which sum to -b = -2.
(You will note that the numbers used in the binomial factors are the opposites of the roots x1 and x2 in the Viete's Formulas. That is how we can look for them to sum to "b", rather than "-b".)
