A rectangle has sides of x + 3y and 4x - y
We had to find the area so (x + 3y)(4x - y) = 4x^2 + 11xy + 3y^2
Then we were asked to find the domain of x (so like what x COULD be). How do you find this?
The answer is x > -3y
How do you get this answer? What are the steps and can this be applied to other questions similar to this? I don't really understand so if you could show your working out that'd be great, thank you!
How to find the domain of this algebraic question? Easy?
2015-02-23 6:09 am
回答 (2)
2015-02-23 6:12 am
✔ 最佳答案
Firstly, your calculations are incorrect...(x + 3y)(4x - y) ≠ 4x² + 11xy + 3y²
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Rather,
(x + 3y)(4x - y)
= x(4x - y) + 3y(4x - y)
= 4x² - xy + 12xy - 3y²
= 4x² + 11xy - 3y²
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Also, your textbook is incorrect.
The domain is not x > -3y
The domain is (-∞, ∞) <-- x and y can be all real numbers!
2015-02-23 6:20 am
true , the text answer is not valid...but it is not all reals for x...
both x ≥ - 3y and x ≥ y / 4 are needed...so x ≥ max { y / 4 and - 3y }...as
the sides are not negative...using just the equation then both x & y can be anything
both x ≥ - 3y and x ≥ y / 4 are needed...so x ≥ max { y / 4 and - 3y }...as
the sides are not negative...using just the equation then both x & y can be anything
收錄日期: 2021-04-21 01:21:28
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