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Maths Question

Find two integers whose sum is 4 and product is -45
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Avatar for mqb2766
mqb2766
21
Original post by iHateHegartyMath
Find two integers whose sum is 4 and product is -45


Look at the factors of 45 and its fairly straightforward.
-5×9
9-5
Original post by kerry0013
-5×9
9-5

Cheers Kerry! :smile:
Original post by iHateHegartyMath
Cheers Kerry! :smile:


um have I say something wrong? is that comment sarcastic!? I mean I'm just replying a question...
Please read the rules and do not post solutions :smile:
Original post by kerry0013
um have I say something wrong? is that comment sarcastic!? I mean I'm just replying a question...


Im not being sarcastic, just saying thank you
Original post by iHateHegartyMath
Find two integers whose sum is 4 and product is -45

xy=−45xy=-45

x+y=4x+y=4

∴x+y=x+−45x=4\therefore x+y=x+\frac{-45}{x}=4

Rearrange to a quadratic, and solve.
Original post by iHateHegartyMath
Im not being sarcastic, just saying thank you


oh great then... it's the least I can do❤❤❤ lots of love
Reply 9
Avatar for Notnek
Notnek
21
Original post by RogerOxon
xy=−45xy=-45

x+y=4x+y=4

∴x+y=x+−45x=4\therefore x+y=x+\frac{-45}{x}=4

Rearrange to a quadratic, and solve.

But to solve the quadratic you need to find two numbers which add to 4 and multiply to -45 :smile: It's quicker to just look for the numbers.
Original post by RogerOxon
xy=−45xy=-45

x+y=4x+y=4

∴x+y=x+−45x=4\therefore x+y=x+\frac{-45}{x}=4

Rearrange to a quadratic, and solve.

Algebraic approach is not needed here ,,,
Original post by Sir Cumference
But to solve the quadratic you need to find two numbers which add to 4 and multiply to -45 :smile: It's quicker to just look for the numbers.

True, but a quadratic can be solved by using the quadratic formula. It's a general approach that will work with any numbers - they just happen to be easy here.
Original post by RogerOxon
True, but a quadratic can be solved by using the quadratic formula. It's a general approach that will work with any numbers - they just happen to be easy here.

This is from a Foundation paper so that approach isn't needed; the formula is really for questions with non-integer solutions.
Original post by Muttley79
This is from a Foundation paper so that approach isn't needed; the formula is really for questions with non-integer solutions.

I agree, although people sometimes panic in exams, or miss the obvious, so it's good to know the algebraic approach.

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