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secondary 3 | A Maths
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help would be greatly appreciated asap!!
Date Posted: 2 years ago
Views: 180
Alternative approach (since I see two of the 2 - x)
-6x² - 17x + 28 = A (x + 5) (2 - x) + B (2 - x) + C
When x = 2 (I picked x = 2 for a reason...),
-6 (2)² - 17 (2) + 28 = A (2 + 5) (2 - 2) + B (2 - 2) + C
-24 - 34 + 28 = A (7) (0) + B (0) + C
-30 = C
-6x² - 17x + 28 = A (x + 5) (2 - x) + B (2 - x) - 30
There is going to be only one combination on the right-hand side leading to an expression in x². Which one is it?
It's A multiplied by x from the first bracket multiplied by -x from the second bracket.
Comparing terms in x², -6x² = A (x) (-x)
We get A = 6.
-6x² - 17x + 28 = 6 (x + 5) (2 - x) + B (2 - x) - 30
Now that we have one unknown left, it's free and easy.
When x = 0 (I picked zero for a reason...),
-6 (0)² - 17 (0) + 28 = 6 (0 + 5) (2 - 0) + B (2 - 0) - 30
-0 - 0 + 28 = 60 + 2B - 30
28 = 30 + 2B
-2 = 2B
-1 = B
So, we get A = 6, B = -1 and C = -30.
The expansion way is probably easier for you, but I believe that your teacher would like you to use substitution of x = 2 in view of the (2 - x) being written twice,
-6x² - 17x + 28 = A (x + 5) (2 - x) + B (2 - x) + C
When x = 2 (I picked x = 2 for a reason...),
-6 (2)² - 17 (2) + 28 = A (2 + 5) (2 - 2) + B (2 - 2) + C
-24 - 34 + 28 = A (7) (0) + B (0) + C
-30 = C
-6x² - 17x + 28 = A (x + 5) (2 - x) + B (2 - x) - 30
There is going to be only one combination on the right-hand side leading to an expression in x². Which one is it?
It's A multiplied by x from the first bracket multiplied by -x from the second bracket.
Comparing terms in x², -6x² = A (x) (-x)
We get A = 6.
-6x² - 17x + 28 = 6 (x + 5) (2 - x) + B (2 - x) - 30
Now that we have one unknown left, it's free and easy.
When x = 0 (I picked zero for a reason...),
-6 (0)² - 17 (0) + 28 = 6 (0 + 5) (2 - 0) + B (2 - 0) - 30
-0 - 0 + 28 = 60 + 2B - 30
28 = 30 + 2B
-2 = 2B
-1 = B
So, we get A = 6, B = -1 and C = -30.
The expansion way is probably easier for you, but I believe that your teacher would like you to use substitution of x = 2 in view of the (2 - x) being written twice,
See 1 Answer
done
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compare coefficients!
Date Posted:
2 years ago
That's wrong it should be B- C?
I don't see anything wrong with the tutor's workings and he did not copy the question wrongly.
I have confirmed this using the Symbolab software
What do you mean by "B - C'? Which line?
I have confirmed this using the Symbolab software
What do you mean by "B - C'? Which line?
thank you !!
I mean if you multiply the x by the y square then add in B- put it into C B- -C
There is no y here. You might have looked at a different question rather than this one.
Yea idk
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