To find the answer to "What two numbers have a product of 90 and a sum of 78?" we first state what we know. We are looking for x and y and we know that x • y = 90 and x + y = 78.
Before we keep going, it is important to know that x • y is the same as y • x and x + y is the same as y + x. The two variables are interchangeable. Which means that when we create one equation to solve the problem, we will have two answers.
To solve the problem, we take x + y = 78 and solve it for y to get y = 78 - x. Then, we replace y in x • y = 90 with 78 - x to get this:
x • (78 - x) = 90
Like we said above, the x and y are interchangeable, therefore the x in the equation above could also be y. The bottom line is that when we solved the equation we got two answers which are the two numbers that have a product of 90 and a sum of 78. The numbers are:
1.17144
76.82856
That's it! The two numbers that have a product of 90 and a sum of 78 are 1.17144 and 76.82856 as proven below:
1.17144 • 76.82856 ≈ 90
1.17144 + 76.82856 = 78
Note: Answers are rounded up to the nearest five decimals if necessary so the answers may not be exact.
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