Grade 11 math question

[Steven G]

[MATH](d - 3)^2 = (d - 3)(d - 3) = d(d - 3) - 3(d - 3) = d^2 - 3d - 3d + 9 = d^2 - 6d + 9.[/MATH]
[MATH]\sqrt{d^2 - 6d + 9} = \sqrt{(d - 3)^2} = d - 3.[/MATH]
When you have something inside a square root, it is always a good idea to look ro see whether it is a square of something so you can simplify.

It just gets to me to see in print that [math]\sqrt{(d - 3)^2} = d - 3[/MATH]

 

[JeffM]

It just gets to me to see in print that [math]\sqrt{(d - 3)^2} = d - 3[/MATH]

Yeah, I screwed up. But honestly, when you are being asked why x^2 - 6x + 9 = (x - 3)^2 as an 11th grade math question, not all the synapses can fire correctly.

I am off to the corner for either plus or minus (d minus 3) minutes.

 

[Steven G]

g(x) = sqrt{x^2 - 6x + 9} - 3.

This is the original formula. I don't know what happened to the +9 -3

You have to have a better command of what the equal sign means.

You agree that (d-3)^2 = (d^2-6d+9) so what is the problem? You ask where is the 9? Well, just multiply out (d-3)^2 and see what you get. For the record, you'll get d^2-6d+9! Why, because they're equal!

 

[Steven G]

Yeah, I screwed up. But honestly, when you are being asked why x^2 - 6x + 9 = (x - 3)^2 as an 11th grade math question, not all the synapses can fire correctly.

I am off to the corner for either plus or minus d minus 3 minutes.

I never said that you were wrong. I too get that this is for an 11th grade student and your answer is probably appropriate. I just said seeing what you wrote in print gets to me.

 

[JeffM]

I never said that you were wrong. I too get that this is for an 11th grade student and your answer is probably appropriate. I just said seeing what you wrote in print gets to me.

Deservedly. I was wrong. I have no excuse, but I do have an explanation.

I was getting exasperated. This was a student who apparently is studying functions (admittedly at the very threshold) and who does not know FOIL or how to factor a quadratic. The teacher that gave her a passing grade out of pre-algebra should be taken out to the parking lot during recess and trampled to protoplasm by elephants high on psychotropic drugs to the cheers of the abused students. This is why students say “I am terrible at math.” Some idiot teacher just moved them on deeper and deeper into math when someone should have seen the students were floundering with the concept of a variable and needed help before being sent into deeper waters.

 

[Harry_the_cat]

Deservedly. I was wrong. I have no excuse, but I do have an explanation.

I was getting exasperated. This was a student who apparently is studying functions (admittedly at the very threshold) and who does not know FOIL or how to factor a quadratic. The teacher that gave her a passing grade out of pre-algebra should be taken out to the parking lot during recess and trampled to protoplasm by elephants high on psychotropic drugs to the cheers of the abused students. This is why students say “I am terrible at math.” Some idiot teacher just moved them on deeper and deeper into math when someone should have seen the students were floundering with the concept of a variable and needed help before being sent into deeper waters.

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