Q10a (1 Viewer)

[sdx91]

hey ppl

just wondering if i got it right lol.
i did the area of the rectangle - area of curve to get the shaded part? is that the correct way?

thanks.

 

[MrKim]

Thats what i did. I ended up getting 19 something something units squared or something like that, i cant really remember.

 

[smozdaddy]

i got 5ln5 - 4 i believe in the end.

 

[sdx91]

i got 5ln5 - 4 i believe in the end.

i think i got that

 

[iluvGG]

ahh i did that. but forgot to make x the subject!!!!! so i couldnt integrate it!! damn. hope i can get a few of the marks out of 5!!

 

[Rampager]

i got 5ln5 - 4 i believe in the end.

truth.

Area of Rectangle - Unshaded Area bound by Y-Axis = Shaded Area

 

[cond42]

hmm i didnt do it the way most people did.
I used the fact that if you differentiate (x-2)ln(x-2) then u get ln(x-2) + 1, then did integral from 3 to 7 of ln(x-2) + 1 minus integral from 3 to 7 of 1, using (x-2)ln(x-2) as the primitive of ln(x-2) + 1. I still got 5ln5 - 4, so would this be a justifiable method(seems i still found the area, what the question asked), and do u think i would get 5/5 (or what would i get?).

 

[Timothy.Siu]

hmm i didnt do it the way most people did.
I used the fact that if you differentiate (x-2)ln(x-2) then u get ln(x-2) + 1, then did integral from 3 to 7 of ln(x-2) + 1 minus integral from 3 to 7 of 1, using (x-2)ln(x-2) as the primitive of ln(x-2) + 1. I still got 5ln5 - 4, so would this be a justifiable method(seems i still found the area, what the question asked), and do u think i would get 5/5 (or what would i get?).

i used that method to check, but i used the 2unit one to do it

 

[cond42]

do i still get 5/5?

 

[henry08]

i got 5ln5 - 4 i believe in the end.

same

 

[stormz89]

I completely forgot how to integrate lnx

I stared at it for like 15mins not knowing what to do. So I gave up and wrote this.

Loge(x-2) told me it didn't wanted to be integrated when it was 3, we grew up together. Now it went to college, doesn't call me anymore. What a jerk.

And just left the exam room (in the proper way after checking my previous answers)

 

[betraya]

I did it by knowing the integral of lnx = xlnx-x and thus getting 5ln5 -4

 

[cond42]

I did it by knowing the integral of lnx = xlnx-x and thus getting 5ln5 -4

yeah you seem to have done the same as me, this is a correct method to use isnt it?...it would be kinda stupid if it wasnt but u never know...do u reckon we get 5/5?

 

[kwinnall]

I completely forgot how to integrate lnx

I stared at it for like 15mins not knowing what to do. So I gave up and wrote this.

Loge(x-2) told me it didn't wanted to be integrated when it was 3, we grew up together. Now it went to college, doesn't call me anymore. What a jerk.

And just left the exam room (in the proper way after checking my previous answers)

LOL

 

[betraya]

of course. When i got marked wrong in my trial for a similar question involving integrating log x dx between 7 and 4 my teacher argued about it to the other teachers. He said to me that the board of studies markers would mark that method correct cause it's such a better and time efficient way than using rectangle minus the other bit.

 

[cond42]

sweet hope your teacher's right! lol

 

[zvyx]

Rarely do you see 5 markers.. so I was put off by that in the reading time..
Then I looked at the question briefly, thought it was piece of cake. "5 marks woo" I thought.
45 min to go, I reach question 10, look at it and think "wtf integrating lnx?"

but yeh. I reflected the graph along y=x, thus giving y = e^x + 2, and did the area of rectangle etc stuff. 5ln5 - 4 all the way

 

[farkmedead]

yeah, umm i think the rectangle was 7ln5 and the shaded region was 2ln5+4 or something
so 7ln5-(2ln5+4)=5ln5-4 i can't remember too well but/.

 

[sasha279]

Rarely do you see 5 markers.. so I was put off by that in the reading time..
Then I looked at the question briefly, thought it was piece of cake. "5 marks woo" I thought.
45 min to go, I reach question 10, look at it and think "wtf integrating lnx?"

but yeh. I reflected the graph along y=x, thus giving y = e^x + 2, and did the area of rectangle etc stuff. 5ln5 - 4 all the way

Do you mean x = e^y + 2?

Yup I also got 5ln5 - 4 ^^

 

[Azreil]

I completely forgot how to integrate lnx

I stared at it for like 15mins not knowing what to do. So I gave up and wrote this.

Loge(x-2) told me it didn't wanted to be integrated when it was 3, we grew up together. Now it went to college, doesn't call me anymore. What a jerk.

And just left the exam room (in the proper way after checking my previous answers)

I did also. Completely blanked out. Left it, did part b) then came back and was like "Ah, Mr Curran's magical method of magic!" and did the rectangle - the curve.

Though I did lol at your answer :]