algebra

[edwindelasacha]

I need to find the value of y:

2.2= y+1.27/y^2

 

[wjm11]

I need to find the value of y:

2.2= y+1.27/y^2

What methods have you learned? What methods are you studying in school right now? What have you tried so far? We need to know these things in order to help you. Also, just to be clear, is your problem 2.2= (y+1.27)/y^2 , or is it 2.2= y+(1.27/y^2)? I just want to be clear on the numerator.

 

[HallsofIvy]

In either case, I would recommend multiplying both sides by \(\displaystyle y^2\) to just get rid of the denominator.

 

[edwindelasacha]

What methods have you learned? What methods are you studying in school right now? What have you tried so far? We need to know these things in order to help you. Also, just to be clear, is your problem 2.2= (y+1.27)/y^2 , or is it 2.2= y+(1.27/y^2)? I just want to be clear on the numerator.

I am studying Civil Engineering 4th year at uni, not the best at maths and couple of friends can get it either apart from trying figures until 2.2=2.2 on both sides. Presuming the BODMAS rule applies I mean 2.2= y+(1.27/y^2).

 

[JeffM]

I am studying Civil Engineering 4th year at uni, not the best at maths and couple of friends can get it either apart from trying figures until 2.2=2.2 on both sides. Presuming the BODMAS rule applies I mean 2.2= y+(1.27/y^2).

Yes, the PEMDAS convention (as we call it in the US) applies, but about 90% of the questions posed violate it so we like to make sure.

\(\displaystyle 2.2 = y + \dfrac{1.27}{y^2} \implies 2.2y^2 = y^3 + 1.27 \implies f(y) = y^3 - 2.2y^2 + 1.27 = 0.\)

There are at least three ways to find the roots of any cubic. Look up and use the cubic formula (ugh). Graph f(y). Use the Newton-Raphson method of successive approximations to find the roots. It is clear by inspection that there is a root between - 1 and 0 so you can start the NR method with a decent initial approximation of minus 0.5.

Do you know the Newton-Raphson method? I'd think it would be super-handy for engineers to know. (You must take that comment with a bushel of salt: my academic training was in history.)