quick show question (1 Viewer)

[fullonoob]

show that 1/ (x^2 -9) = 1/6 (1/(x-3) - 1/(x+3))
i . e

you cant go backwards right

 

[ohexploitable]

 

[solomarc20]

With show questions, it doesn't matter which side you start with. If you can get to the line LHS=RHS, either from starting from the LHS or the RHS, then it has been done

 

[AAEldar]

ohexploitable is correct. All your doing is getting the same denominator inside the brackets by cross multiplying, then simplifying that result. Then cancelling down the 6's in the fractions.

 

[hscishard]

And when you use one side, you can't modify the other. Choose carefully. Lol

 

[fullonoob]

i remember my maths teacher said you always have to go from LHS = RHS. If you do RHS = LHS you get zero, when marked by strict HSC markers.

 

[lychnobity]

i remember my maths teacher said you always have to go from LHS = RHS. If you do RHS = LHS you get zero, when marked by strict HSC markers.

Don't listen to him.

 

[fullonoob]

how about if it says "prove". Then you must go from LHS to RHS?

 

[Lolsmith]

It doesn't matter. They both should equal each other, so RHS = LHS and vice versa.

 

[hscishard]

Yea prove is definitely LHS to RHS

 

[thongetsu]

yeah rhs=lhs and lhs=rhs is the SAME thing!

 

[hscishard]

:S most maths textbooks do LHS to RHS. Too confusing. Who's correct? The book or the human?

 

[Lolsmith]

It's encouraged to do LHS to RHS, but there's no real difference. I sincerely doubt that any teacher or marker would mark you incorrect for proving something equals something but did it with a different side than the previous person.




...Unless they hate you.

 

[hscishard]

from now on, I'm going to do the easier way, but if I did RHS = LHS I'll just write everything backwards - forwards. Then put therefore true, LHS = RHS

 

[thongetsu]

mmmm showing/proving is one of the easiest maths questions considering you are given the answer

 

[hscishard]

I personally find them hard. But the induction questions are easy. Weird

If it was so easy, why wouldn't textbooks provide the "show" answers in the answers section?

 

[thongetsu]

because it's too easy? only the working out is required and it's usually fairly basic. also i find induction easy too

 

[Aquawhite]

I always had this misconception too. You do not need to prove that LHS = RHS in any particular order. Often, the best choice, is to make the bigger one, smaller.

Usually, you will find that HSC questions are often just trig stuff, which gets easier with practice.

 

[AAEldar]

I've always been taught to look at whatever side you can do easier. Since LHS=RHS and vice versa, it shouldn't matter what side you do first.

 

[Carrotsticks]

i remember my maths teacher said you always have to go from LHS = RHS. If you do RHS = LHS you get zero, when marked by strict HSC markers.

This is incorrect. Many Trig identity questions require that you start from RHS.