MHB Applying quadratic formula to inverse of a function: Calculation problem

AI Thread Summary
The discussion centers on clarifying the steps involved in applying the quadratic formula to find the inverse of a function, specifically addressing a simplification issue in a math textbook. The user initially struggles with understanding how to divide terms by -10, particularly under a square root, and how the expression simplifies from 20 to .2 while leaving (60-h) unchanged. After some reflection, the user realizes that dividing each term by -10 systematically leads to the correct simplification. The final expression shows the correct handling of the square root and the coefficients involved. This highlights the importance of following the order of operations in algebraic manipulations.
self4u
Messages
2
Reaction score
0
Hi - I'm trying to figure out the specific steps in a math textbook. I'm trying to figure out how the textbook did its algebra here with a quadratic formula to find an inverse of a function:

View attachment 5796

Sadly there's a step I'm supposed to know by now in the simplification algebra in there 3 steps shown...and I'm missing it.

From step 2 to step 3...it looks like only part of the equation is divided by the denominator -10. I didn't think it was possible to divide by 10 with individual numbers under the square root symbol. Furthermore - step 3 shows a reduced ".2(60-h)". How did 20 go to .2? How is (60-h) completely unaffected?

Sorry for such a simple question and thank you in advance for your help!
 

Attachments

  • quadhelp.JPG
    quadhelp.JPG
    5.2 KB · Views: 118
Mathematics news on Phys.org
Okay I think I've finally figured it out. I'm a dolt. But since I'm a dolt, I might as well post why I'm a dolt due to the order of operations.

Step 2A: Simply divide every single number by -10. So the method to get to Step 3 becomes:

a) (-30/-10) which becomes positive 3.

b) Then (30sq./-10) which becomes -3sq...then becoming 9.

c) Then (20/-10) which becomes -2.

d) Then (60/-10) which becomes -6. At this point we could multiple it with the (-2) above making positive 12.

e) Then (h/-10) which becomes -h/10. At this point we could multiple it with the (-2) above making -2/10h...simplified to -1/5h...or -.2h.

That gets to step 3...remembering to keep the square root above 21 - .2h.
 
$$\begin{align*}\dfrac{-30\pm\sqrt{30^2+20(60-h)}}{-10}&=3\pm\dfrac{\sqrt{30^2+20(60-h)}}{-1\cdot|10|} \\
&=3\pm\dfrac{\sqrt{30^2+20(60-h)}}{-1\sqrt{10^2}} \\
&=3\mp\sqrt{\dfrac{900+20(60-h)}{100}} \\
&=3\mp\sqrt{9+\dfrac15(60-h)}=3\mp\sqrt{3^2+.2(60-h)}\end{align*}$$
 
Suppose ,instead of the usual x,y coordinate system with an I basis vector along the x -axis and a corresponding j basis vector along the y-axis we instead have a different pair of basis vectors ,call them e and f along their respective axes. I have seen that this is an important subject in maths My question is what physical applications does such a model apply to? I am asking here because I have devoted quite a lot of time in the past to understanding convectors and the dual...
Insights auto threads is broken atm, so I'm manually creating these for new Insight articles. In Dirac’s Principles of Quantum Mechanics published in 1930 he introduced a “convenient notation” he referred to as a “delta function” which he treated as a continuum analog to the discrete Kronecker delta. The Kronecker delta is simply the indexed components of the identity operator in matrix algebra Source: https://www.physicsforums.com/insights/what-exactly-is-diracs-delta-function/ by...

Similar threads

Replies
7
Views
3K
Replies
4
Views
4K
Replies
5
Views
1K
Replies
3
Views
4K
Replies
3
Views
3K
Replies
2
Views
4K
Replies
4
Views
2K
Back
Top